Some more on pronunciation

Having "native-like" spoken English is not a must. But being able to differenciate specific sounds is, though. The other day, a student of mine said he'll never /shit/ on his girlfriend. Well... I really hope not!
In the very same class another guy said it would be hard for him if he had to /shoes/ between his girlfriend and his carreer.
Yet another one said he was late because he had to /chop/ with his mom. I suppose she needed some help in the kitchen...

For that reason, being familiar with phonetics can help. A lot. Actually, more than students imagine. For you guys that don't have a clue of what I'm saying this page here is a good start.

However, the most amazing of all, in my humble opinion (I'm saying that as an English teacher and a former speech therapist) is this page, produced at the University of Iowa. I say amazing because it's instructive, clear and - overall - complete.
There are also pronunciation tips at this BBC page and a free phonetics course (for Portuguese speakers) here. It's really handy!

And if you feel like studying some more about pronunciation, there's pretty much everything in here, as well as all around the net. Just google around!