I've got the 70-200 non HSM for pentax. It's a nice lens but is pretty heavy. I was talking w/ Zaphod about it earlier. I bought it mainly for weddings but I've used it just snapping around at other events too. It's a little soft at the end of the focal range wide open, but I think most are. It's sometimes difficult to use w/o a tripod indoors unless there's a lot of light b/c you need a shutterspeed > 1/200 to avoid camera shake. Not an issue too much if you increase ISO. I like it and it's a nice lens, I just don't use it as much as I should. I considered selling it and buying a pentax 77mm 1.8 since it's geared more for portraits which is more my interest right now, but I'm still hanging on to it for now. I don't think I would find another new one for the $600 I bought it for.
It's a good purchase to have in your arsenal though. I recently got the 24-70 2.8 and it's pretty much my everyday lens right now. Really happy w/ that one.