I rarely used it in P7 and never with raytracing on. Now in PP 2012, it's not such a big deal.

The hair is indeed a monster but, mostly at the load/delete time. I uncheck "emit light" and leave the rest on. Hair does not need to "emit" in most cases and loses the dreaded IDL precalculation*.* I find this bearable at rendertime and the shadows are great to have finally.*