http://www.bigblueball.com/forums/aim-support/39705-aim-buddy-info-stored-server.html
that link describes aim buddy profile storage. in short, buddy lists are and always have been stored on AIM servers, but profiles behave erratically unless you use AIM 6.x. im not sure how ichat broadcasts itself to AIM, but it's most likely as aim 5.x or not a version of aim at all.
aim 5.x uploads your profile to aim servers on sign on and when editing the profile through aim 5.x. this profile, whether it is blank or not, overwrites the profile that may/may not be saved on aim servers. so if ichat registers itself as aim 5.x (probably) then it overwrote your saved aim profile with a blank one. aim 6.x is smart enough to not do this... but i'd say that's the only reason i would ever use aim 6.x, and it's not enough to move me from adium
copy over all the ichat related files from these locations and you should be good:
/Home/Library/iChat
/Home/Library/ApplicationSupport/iChat
/Home/Library/Preferences (anything iChat related)
i got this info from this link:
http://discussions.apple.com/thread.jspa?messageID=1872713
read through it. it discusses migrating apps from PPC to intel macs, but the principles are the same as intel to intel.