Works with no problems. MP 5,1 12-core, did clean install as always, installed onto RAID0 SSD + Tempo Card for boot, the installer actually worked correctly this time around (Unlike Lion and Mountain Lion, both of which failed to install to RAID0 and required installs to a single drive, then cloning to RAID).
Overall system responsiveness is much faster.
It's caching like crazy, out of 48GB RAM, I'm getting about 28-32GB in use, while just running normal apps, the OS finally seems to be doing something useful with all that RAM.
No significant problems. Apps which have not been specifically updated for Mavericks continue to work as expected.
Very happy with it!
Except OS/X server, which broke VPNs, but it's not critical for me personally.
iTunes sync is gone, but OS/X server kind of takes care of local syncing, so it'd been fine after setting it up to sync my contacts, calendars, etc, to iPhone and iPad (No thank you to uploading personal information into iCloud, which is the only sync option in Mavericks. Endless thread here:
https://discussions.apple.com/message/23643652?ac_cid=tw123456#23643652 75 pages and counting).