I treated myself to a set of Options Oct/Nov 07 and LOVE them! I added a few sets of the Harmony tips a couple of weeks ago just because I was dying to try them (and they're SO PRETTY! LOL). The ONLY time I ever use my straight needles anymore are if I'm just playing with new yarn, trying to find a stitch pattern and gauge I like. It's easier just to fiddle with straights instead of screwing and unscrewing the tips. Other than that, I knit EVERYTHING on my Options. It really is no different knitting flat on the circulars than on straight needles. You just turn and flip the same way.
Did I mention I LOVE my Options!?