Serial ATA on-board might be a waste right now, Insane, but, IMHO, not for that reason.

Sure, the performance won't be any better, but heck, the hard drives we've got right now *can't* go any faster anyhow. Limited by the PCI bus or not, the hard drives will have to be the ones to up the throughput from their ends.
Personally I'd just like to take advantage of the significantly smaller cables. But, to use those cables now, I'd need an adapter to my current ATA drives, which I'd rather not bother with. I'll wait 'til legitimate, hopefully faster, serial ATA hard drives start hitting the market next year.
Edit: Question...the board spec lists "Promise PDC20376...1 ATA100/133 IDE port with RAID0/1". Now, with only one IDE channel for RAID capabilities...wouldn't you take a performance hit with having one drive as master and the other as slave, RAIDed together? I was under the impression that the best way to set up two RAIDed drives was to put them on separate channels, given the way current IDE connections work. Maybe I'm just being silly.