Nathan's been in the toddler room now for two weeks, and I could tell after the first week it had an impact on his speech. I think being around other kids helps him learn how to say new things...for example, he uses full sentences now, even though they are still hard to understand:
"I wanna p(l)ay"
"I want down"
"Mama play choo choo!"
Its very interesting that he has started using "I" now...he also is a big copy cat, and we can get him to try to say most anything if we make it into a copycat game. But, if you ask him to say something, he won't do it!