Erik,
Firmtek (Kim specifically) does not recomend the use of Seagate or Maxtor HDs with their SATA cards. The SSC is an issue but according to her there are some other issues as well that keep the two from playing nice. I had the exact same question when I got mine. I ended up with a Hitachi 500GB deskstar per Firmteks suggestion and have been very pleased. Hope this helps.
Cheers,
Chris
P.S. Hitachi just announced the 7K1000 HD. 7200 RPM, 32 Mb cache, perpendicular drive technology, and 1TB of space. I WANT ONE!
1.4 GHz "digital audio",1.5 GB RAM, 500 GB SATA HD, Firmtek Seritek 1V4 Mac OS X (10.4.8) Pioneer DVR-111D, BFG 6800 GT oc, 30GB 5.5G video, 4GB 1G nano