If you have a 1st gen i7 its a marginal upgrade.
I have a i7 920 @ 4GHz, I might be upgrading to a IB-E+x79 when they come out in September. Not for a super increase in performance, it seems like the last platform before things start getting restrictive in terms of built in DRM and my s**ts gettin' old.
There are rumors of AMD coming out with something competitive, but that could be just more fanboy FUD. IMHO AMD provides a solid product and is great for people who see PC's as Facebook machines (Web with the occasional word processing task). For gamers and people who need speed Intel+Graphics Card offers superior performance now.