I run PT9.0.5 on win7 64bit in my home studio and have PT9.0.3 running on my XP pro sp3, HP dual core laptop so I can mess with stuff while on the road (for my real job) or just not in the studio.
Not big sessions yet thow, 15 audio tracks, a few midi tracks, a couple VSTi but they are growing fast.....!!!
I have all my sessions on a USB ultra ATA 300gig drive (stored in a little zipper case complete with a slot for my iLock), fly stuff from studio to laptop, very mobile and practical, so far have had no issues but like I said, my sessions aren't that big yet.
Cheers
Rob