I was running rEFIt on a MacBook Pro (late 2009, 13", 2,53 GHz) with a WD Scorpio Blue 500 GB HD and OSX 10.5(.8), Windows XP and Ubuntu 10.10...
and everything was working fine!
Then I replaced the HD with a Seagate Momentus 7200.5 750 GB 7200 rpm HD (ST9750420AS; NOT a Momentus XT SSD hybrid)... and the trouble began:
Each time I install rEFIt, my MacBook freaks out... with different symptoms: Sometimes usbmuxd constantly respawns, WindowServer crashes,
and/or mDNSresponder hangs... sometimes the system doesn't boot but hangs at the spinning wheel. And every 2 or 3 boots, HD utility reports a
corrupted disk... similar to Bug ID 3143295.
Over the last weeks, I tracked the error down: Installed 10.6, 10.6.3, 10.6.4, 10.6.5; everything works perfectly fine until I install rEFIt.... see above.
It looks like rEFIt has some trouble with the 4k-instead-of-512b-Sector stuff of newer/larger hard drives: See also 3016982, 3039932 and 3143295!