Obviously it will help, but probably not in all areas equally. My best guess is that it will help the QBs and receivers the most. It's tough for them to throw much outside in the winter, but with the IPF they can practice all winter. I remember at the beginning of Spring practice a year ago Isphording commented that he felt the quarterbacks and receivers were a couple months behind where he would like them to be, and he felt that if the IPF had been done earlier it would have been a great help. In the recent video interview with Vick, he comments that they are "lightyears ahead of what we were last Spring".
http://www.ohiobobcats.com/sports/m-footbl/spec-rel/03121...

The same would probably apply to the kickers, punters, long snappers, and holders.

The other benefit would be the actual spring practices. When the weather is nice, they will practice outside, but in March/April that isn't always true. On those wet/cold spring days, I imagine they can get a lot more done inside.