MBP 13" with XT 500Gb: had it two or three weeks now, and it's starting to impress.... although at first my boot times increased from around 40 seconds to almost 2 minutes. Turned out that somehow my MBP was trying to boot from network first, then HDD. Once I'd sorted this, things now dropped down to around 30s (give or take).
Sound: yes, I can hear it. It's not intrusive but in a quiet room it is audible, and it doesn't appear to spin down regardless of OSX power settings.
Performance: very good, though not as good as a dedicated SSD. Win 7 Enterprise N under Parallels 5 is now usable on my machine
Battery life: under rev23, dropped from say 5 hours to around 2 hours. Can't be certain whether the update to rev24 has helped, although I think it might have crept back to 3 hours, which (for a machine which is predominantly desk bound => connected to mains) isn't a major problem. And perhaps they can fix the spin-down thing*.
* ps. anyone else noticed this, or just me?