I adore my ST20G5. I don't regret getting it over the SN25P, although that one was a great choice as well. It's currently holding:
AMD 64 3000+ @ Stock (No OC yet)
1 GB Corsair PC3200
Seagate 120 GB
Using Xpress 200
My sole purpose of it was to give a PC to my sister while having room for expandability. The onboard stuff is great, even the audio to my surprise.
Rock-solid from the get go (after the necessary BIOS update though). I can even put my desktop's 7800GT in there for instant LAN Gaming-box!
My plans for it include overclocking and throwing in a next generation R520 or R580 based AIW card for multi-media purposes.
I may pick up an X2 3800+ for it when they drop down further in price. (Got 2, so why not one more?
)