What we need to correct the most
This is a question to our more fluent and native Spanish speakers out there. What is the one predominant grammar or speech problem(or mistake) that visitors make when in your country? The one thing that many of you notice that you would like us to change. I would like the advice in hopes it can set us apart from so called "phrase book visitors" Thank you so much in advance.
9 Answers
As anyone who has been here for more than 10 minutes has discovered, Heidi has quite the aversion to non-native speakers' use of subject pronouns.
Specifically, the abundant use of unnecessary subject pronouns, e.g., "Yo estoy comiendo," "Nosotros viviamos en Florida," and "¿Tú estás listo?"
She, and other native speakers from whom I have learned Spanish, tell me that this is the quickest way (apart from the mispronunciation of vowels) to tell that someone is not a native speaker.
Many, many SpanishDict members can attest to how quickly the use of SPs can land them in the Dunce Corner.
P.s. For those Dunce Corner residents, Echoline, Matt, Q, etc., please stay tuned for some big news that I will announce on New Year's Eve. 
OK..Enough of bashing the United States.
I cannot answer first hand, but to get the ball rolling with a second hand answer:
At a Christmas party two weeks ago, I met someone whose family was from Argentina (I am not sure whether he was born in the US or there, but he spoke English with an American accent indistinguishable from mine- and I would guess is in his early 40's). I asked the same question (aimed at pronunciation issues only), and he specifically said that not rolling r's, pronouncing ll as y, and not melding b with v do not bother him that much, but what he has problems with is the way we pronounce the e (too much like a long a).
Unfortunately I did not get to pester him as long as I would have liked so I cannot give more details.
Edit to add: I was specifically asking him to tell me what made us difficult to understand, not what made us sound different- at 47 I know I will never sound like a native speaker, but I also know some foreign accents in English are different, but easily understood, and some impair understanding (I have particular trouble with French accents in English). I was trying to learn what to focus on to make myself understood more easily, not to avoid sounding "foreign".
The biggest problem I noticed in Spain is the pronunciation of the letters in the mouth. In English, sounds are formed deeper in the throat than in Spanish. Many Spanish learners need to learn how to adjust their tongue, and then they will sound more like a native speaker. It takes lots of practice and help from a native speaker would be very helpful to ensure it is done correctly.
One thing I noticed it that you have to open your mouth wide to accomdate the sounds. When I first tried to speak Spanish, my jaw got tired then I realized I was not opening my mouth enough. Tuco is right. Spanish is more concentrated on the mouth then English. That´s why someone said you speak English with a full mouth,but not Spanish.
'OK, that was a lot, as you can see it is a big issue over here :/ But out of curiosity, what makes you say that Americans are more open than British people? It's always interesting to hear someone else's perspective on my country...'
When I say, 'more open' I mean that I think that you Americans, are more able to express your feelings than us Brits. Also, here in Britain we have a different way of thinking, things like the 'it's the taking parts that counts' attitude and our strong use of sarcasm make us who we are as a nation (we mock our friends in a highly weird sort of way like if someone was to introduce their friend Bob to someone else, they might say, 'Oh this is Bob- a bit of a prat!', and laugh it off, I'm not sure I can picture Americans to be like that).
Also, one more thing I'd like to say is that British humour is more subtle....
'I am an American and so I have no qualms saying that, in general, we have terrible accents. It must be that, through Hollywood and major media, we are so accustomed to hearing our own? Or we are so unaccustomed to interacting with and/or learning any languages other than (American) English...'
Maybe...I'm not sure. Actually, what you've said about the major media may well be completely true, the arts I think are more dominated by the USA in general, and so, Americans may not be used to interacting with other cultures, whilst here in Britain, we (although we're less open than the Americans) love to mix with cultures outside our own.
In northern Mexico, close to the American border, it would be expected that most people were bilingual. They're not. Although they have access to American TV and Radio, they'd rather watch Mexican TV and listen to Mexican radio stations. Talking to one guy from Ciudad Jurez (a town just across the US border) he told me that people there are just too apathetic to learn English. Unbelievable. Even Mexicans who have lived in the US for many years are unable to speak English. I guess they value their culture too highly and learning English would challenge it or something like that.
It's a bit like the Pakistanis living in Bradford or Leeds in the UK, many of them don't speak English and the British police are learning Urdu to communicate with them.
Here are some findings which I dug up from the msnbc website. This was from a survey of the general American public:
One-third of respondents couldn’t pinpoint Louisiana on a map and 48 percent were unable to locate Mississippi.
Fewer than three in 10 think it important to know the locations of countries in the news and just 14 percent believe speaking another language is a necessary skill.
Two-thirds didn’t know that the earthquake that killed 70,000 people in October 2005 occurred in Pakistan.
Six in 10 could not find Iraq on a map of the Middle East.
While the outsourcing of jobs to India has been a major U.S. business story, 47 percent could not find the Indian subcontinent on a map of Asia.
While Israeli-Palestinian strife has been in the news for the entire lives of the respondents, 75 percent were unable to locate Israel on a map of the Middle East.
Nearly three-quarters incorrectly named English as the most widely spoken native language.
Six in 10 did not know the border between North and South Korea is the most heavily fortified in the world.
Thirty percent thought the most heavily fortified border was between the United States and Mexico.
Before I begin, I'd like to say that I'm not a fluent Spanish speaker or a native speaker. If I can make one observation- I've noticed that Americans or Westerners in general who learn Spanish, tend to have a strong thickset accent from which you can tell where they're from. I don't mean to cause uproar among the American camp (which seems to be most dominant here), but I have noticed amongst American and British friends and acquaintances, this trait which I find quite strange in a way. I'm British born myself, however my family originates from Afghanistan.
My experience as a foreign language teacher has led me to the conclusion that, in any language, one of the major problems of pronunciation lies in the vowels. Students that practice vowels in Spanish and get them down sound way better than those that rely on using English vowels....In English unstressed vowels tend to relax into a schwa, which is a sound (phoneme) that does not exist in Spanish, creating a greater distinction between a native and non-native speaker.
