Yeah it works well. Although theres no support for tuners at all and I wouldn't expect anytime soon. It's still pretty much identical to XBMC so no Mac spacific features.
If you want to go this way I would probably go with the EyeTV software which intergrates with Frontrow. That along with Perian will get you almost the same playback capabilities of XBMC - along with FreeviewHD.
Personally I'm waiting to Apple lauch either a better AppleTV or a Mini with at least X1300 gfx - so that 1080P out put is possible. For now neither have the power to deal with full HD.