The only "Phenom specific" issue is generally EFi. You need to avoid a distro that uses PC_EFI v8 for the install disk (and most of them do...). For EFi you need Chameleon. Otherwise OSx86 issues for motherboards and chipsets are pretty much the same as they are for other AMD processors.

Here's my Phenom build:
Gigabyte GA-MA78GM S2H v1.1 motherboard
Phenom 9550
Onboard Ati Radeon HD3200 graphics (VESA support, no QE/CI)
LG GGC-H20L "Super Multi-Blu" SATA HD-DVD / Blu-ray / DVD+-RW / Lightscribe optical drive (in IDE mode)
SATA hard drives in AHCI mode
boots from external USB hard drive
Onboard Realtek RTL8111 gigabit LAN
Onboard Realtek ALC889a HD audio
TI 1394a controller
2GB PC8500 DDR2 RAM (1066MHz)

I used Zephyroth 10.5.1 for the initial install (before the lawlessppc release) - it worked because it was before PC_EFI v8 became widely used in AMD circles. Then I used Zephyroth ASU 0.5 to upgrade to 10.5.3 and 10.5.4. I added the Chameleon EFi for AMD K10 (Phenom). Runs great. I get a 175-180 in xbench if I leave off the disk test. Same test using a 2.2GHz dual-core gives 115-120.

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Running both 10.5.8 and 10.6.4 on my stinking AMD/ATi machine...