Just to throw another "personal experience" in
I've got the camera set to "Raw + JPEG" at the moment, and when I read through this post i actually thought to myself "why?". I'm shooting in tricky lighting that i NEED RAW capture for. Why on earth am I taking up card space and subsequently hard drive space with JPEGs as well? Doh!
I agree that one benefit might be that if your copy of windows / whatever can't preview RAW files (i've got the RAW viewer but I think it only handles NEF and CR2 so wouldn't help some users) then the JPEG makes a handy preview. But I really must go and turn it off on my bodies!
My rule of thumb, if it helps any, is JPEG for snaps and RAW for my "serious" stuff. But try it out first and see what works best for you...
HTH!