I've loaded it onto this machine and one other at my house. So far, so good. My only complaint was that it turns on XP's internet connection firewall. My Linux firewall is sufficient (and better), so I turned that back off. (It doesn't ask.) That's apparently caused a number of people trouble with file sharing. I've been reading the horror stories as well, so all is not necessarily well. I've yet to risk it on my work laptop. I'll let it stew here a home for a couple months first. I did the same thing with Service Pack 1. It caused a lot of people problems, too.
If you install it and it does cause problems, you should be able to back it out. It saves all the files it replaces and you can uninstall the service pack to get back. Supposedly anyway. I know it saves the files, but I can't vouch for the going back part. Never had to.
Case: Enermax CS-A106USB
P/S: OCZ OCZ700GXSSLI 700W
Motherboard: ASUS P5N32-E SLI
CPU: Intel E6300(idle 35C/load 39C)
RAM: OCZ Platinum Rev 2 DDR2 800 MHz (4 x 1GB) 4-4-4-15-T1 (2.1v)
Hard Disk: Seagate 2x250GB SATA ST3250620AS in RAID1
Monitor: Mitsubishi DP900u
Graphics: BFG GeForce 8800GT PCI-E
Sound: SoundBlaster X-Fi Fatal1ty
Speakers: Klipsch ProMedia v.2-400 4.1 speakers
Optical: LiteOn 16X DVD-ROM; Sony DRU-710A DVD-RW