I have been wondering this too, but to be honest, I am now questioning the sanity of such a wait for Haswell.
6 weeks and it is released, bugs n all, with a few motherboards. But how long before it is refined, bugs ironed out, or we see CPU revisions, or better motherboards for Haswell ?
I am now thinking it is not worth buying such a new CPU straight away, but wait till it is established, gained it's reviews podiums, and that there is selective high performing motherboards and system reviews to gauge performance and purchase choices by.
Maybe 6 months to a year after release before stable top performance choices of motherboards, CPU's and coolers are available to select from?
There probably won't be revisions of Haswell as Haswell itself is a revision of Ivy Bridge on a new socket pretty much. And you're probably looking at a 5-10% increase again if you're lucky.