Yeah I'd like to wait on that one....
My current main box is a FN41G 1GB RAM and AMD 3200+ and its really nice.....

However i think my first AMD64 is likely to be full form factor.

I recently had a problem with an older shuttle i gave to my girlfriend.
It had a Duron1300 in and had been running fine
However when i gave it her I also had an Old AMD1400+ (1250 Mhz) which I thought would be fine and give her the extra cache and be a bit better for ripping mp3

What a nightmare.....
The 1400+ was one of the very first....
Everytinme she started to rip it powered off.

I tried EVERYTHING, different encoder ... etc. etc.
In the end I guessed it was a power issue. After spending a long time downloading the tech data from AMD and calculating the wattage needed the 1250Mhz used 20% more peak than the Duron....

I replaced it with a 2200+ which uses about 50% of the 1400+ !!!!
and its running perfectly.....

The moral is that early revisions of new chips tend to be power hungry!!
I would expect AMD64 to be a little hot at first!!!

And the shuttle is, well a shuttle.
The PSU is limited, although you can buy uprated ones theyre noisier so eventually you loose that nice pretty quiet thing that is why you bought it!!!

My advice is go for the full form factor until they get cheaper and better unless you REALLY need al that bang in a small box!!