I must admit I'm with Goldorak.
Lynnfield will run on yet another new socket, LGA 1156. It's a direct replacement for the current Penryns. By the time supply is steady, costs should be the same for Lynnfield CPU + P55 board as you would pay now for Penryn + board. It's worth holding out for, but probably means waiting till Q4 before you buy.
The biggest problem moving to i7 right know is that the boards cost 2x as much. 150,- for a basic board, 200,- for a good one. Add 230,- for the 920, and most of the budget is gone already.