I've also heard one of the "benefits" of SATA was, assuming you used the 
special power plugs instead of the standard 4-wire one we all love (and have eight 
of on our power supplies anyway), you'd get hotswappability.  A vital feature 
in a desktop, I know. :P Supposedly, the special plug's more delicate, prone 
to falling out, compared with the old ones.

Aside:  Whatever happened to the "3.5 x 1 inch" form factor for hard discs?  
It would allow an ample heatsink, letting the PCB run cool.  Having to 
organise special cooling on ordinary 7200rpm desktop drives seems a bit absurd.

For speed:  Notice even that expensive, "ultra fast" WD Raptors don't even 
sustain 66Mbps.  That's the celing on the UDMA-66 standard (two generations of 
UATA ago).  The interface doesn't bottleneck right now, in fact it rarely does.