Sorry I'm so late responding to this. I've been on the road, traveling to more of the beautiful cities in Colombia.
Here, Usted and Tu seem almost interchangeable. I often hear friends talking and switching back and forth. Some of that may be the seeming difficulty of some conjugations in the Tu form.
For example, I often hear something like ¿Vas al cine? but I don't recall ever hearing ¿Fuiste al cine? The past tense is a little complicated, so we tend not to use it.
Stores often use the informal form, even in their advertising. On the other hand, some stores or commercial products always use the formal. Por ejemplo: pague 6, lleve 9. (pay for six, take nine)--a sale on paper. Today I was given some Bingo cards at a store (didn't win anything). On the cards it says "busca tu premio" and "sigue participando." All informal.
I guess the bottom line is just what Natasha said. It depends on the country. Back in the 1970s, no one in Caracas, Venezuela would use the informal with strangers, but the folks in Colombia used it all the time.
In any case, my experience in Colombia, and with a number of folks from other Latin American countries, is that if you make a mistake with the language, they'll still understand you and go on. About the last thing they'll want to do is make you feel uncomfortable. I don't know how many times I've had people tell me that I speak Spanish perfectly. They're lying, but it's only to make me more comfortable. Actually, it makes me want to continue to improve my ability with the language.