I'm using SDHC for my music (my girlfriend calls my Mini the world's largest MP3 player ever) and have no problem with the speed. I also run video off the SDHC, and, again, no problem. I haven't tried to do high definition video, though.
The mini is quiet (how could it not be, no moving parts), pretty cool if it gets decent circulation, and has handled everything I've asked it to so far without complaint. You'll probably be happy with it.
Black Mini 9 | 4GB SSD | [s:1kutak77]512MB RAM[/s:1kutak77] | [s:1kutak77]Ubuntu[/s:1kutak77]
RAM: Kingston HyperX 2GB 533MHz DDR2 CL3-3-3-8
OS: Gentoo Linux, ion3 WM