As I have I posted in other thread at MacRumors, my experience has shown me overall the Mini is faster but can absolutely suck at some things in standard OEM form. The standard hdd is a steaming, dog turd and is much slower than the raid 0 setup in my old school PowerMac. A ssd or Momentus XT would be a tremendous improvement. While graphics benchmarks show the 320m to be much better than the 6800 in my PowerMac, real usage has shown otherwise. Overall they seem to perform a little better but once in a while my graphics will lag quite badly when gaming, specifically in WoW and that is with the settings turned waaaay down. Usually a few seconds is all it takes to recover but a few times it never did recover until I restarted the game, which is pretty bad IMO. Other apps seem to run fine.
Also, my Mini gets quite warm when gaming; I would go so far to say borderline 'hot'. Other apps seem fine but I have not used iMovie extensively yet.
In fairness to the 'tiniest Mac', I plan to upgrade the hdd to at least a Momentus XT, possibly a ssd, and also to up the ram to 4 or 8 GB, keeping dual channel intact by not going with 3, 5 or 6 GB. Overall I am satisfied with my Mini and I never expected too much of it. I love the design and how little power it uses and I had a 23" ACD left from my PowerMac dying so I thought, why not get a Mini? The Mini is NOT a workstation not a gaming computer so don't expect miracles, only expect what it should be capable of and you'll be fine.
I hope this helps in any way.
🙂