i am currently running 10.6.2 and i love it. Snow leopard on Mini 9 is stunningly fast and especially at applications like safari, quicktime, bootup, shutdown,emails, front row, etc. After installing 10.6.1 your gonna run into some problems like sound not working for headphones and sleep/wake issues.
For the headphones just use
this method here btw: don't use the voodoo method (i used that first and it slowed down my speed alot and whole system got unstable.
for the sleep/wake issue just run NBI 0.8.2 then 0.8.3 and turn off usb lagecy in bios fixed the sleep issue for me.
Hope this helps.
btw im also using snow leopard on imac so i can say that the mini runs very smoothly and can sometimes match up even to the imac =)