I'm using the version of the smartpower 350 that came with the Antec BQE case. But be careful, I understand that Antec have increased the 12v Amps on new power supplies (according to something I read in this forum). I got a new one, as my 12v supply is rated at 21 Amps (UK version). So if you're planning to use an old version, check the 12v output.
My set-up is very basic:
A8N-SLI (non-deluxe)
3000 Winchester
1 GB (2x512) memory
1 x Leadtek 6600 GT Extreme Edition
1 x Maxtor 120 GB Serial ATA
A couple of optical drives, floppy, PCI wireless card, external firewire Maxtor 150GB drive and a few USB devices.
I've not had a hint of a problem with power (and I don't think I should have expected to with my set up)
Note that you will have to fit the 20 pin connector to the 24 pin MB connector (leave the 4 pins nearest the IDE connetors unconnected). As I was missing the 4 pins, I also plugged in the EZ-plug (or whatever it's called) even though I'm only using one PCI-E card. Don't know if I needed to, but it's not caused any problems.