Part of what mikethesick has to say is true, that they will ask for your i20, and as long as it is valid i.e. not expired and has a recent (6 months) signature on 2nd page, you are fine.

However, I dont agree with mikethesick about visa and i20 being from different instuitions. The whole point of sevis system (remember the $100 we paid for that thing) and i20 is to keep track of us while we jump colleges and universities.

I also agree with the immigration officers not knowing what they are supposed to do. [once this guy made me wait while he went over to a colleague for help, maybe it was his first day]
[I had travelled to Nepal while in college, then to Canada while in OPT]