HSF... until I stopped being lazy and started taking the mobo out of the case to do it, no problem since then. Trying to apply a decent layer of Shin-Etsu was never any extra fun for the proceedings, just stick with the dead easy Alumina now. Never come close to damaging anything when installing a HSF on any of my athlons.
BIOS flash... eek. Once I killed a mobo on my first self-built PC because I had a bad bios file, rescued it about a week later when someone came up with the amiboot.rom trick (a trick the manuf's engineer thanked me for when I passed it on ). A second time on a different mobo, floppy screwed up and it was bad flash, rescuded thanks to gigabyte's dual bios.
bios flashing wins