I really like Adium, but sometimes I have to do a video chat, or conveniently send some files or images, which iChat excels at. So, sometimes I have to easily switch between the two programs. While you can set up iChat (or rather, AIM) to allow connection from separate accounts, I really like to disconnect Adium when I connect iChat. So I wrote an AppleScript that easily switches between them. I looks like this:
tell application "System Events"
set aApps to name of every application process
end tell
if "Adium" is in aApps then
tell application "Adium"
set tAccount to ID of first account whose serviceID is "Mac"
set isOnline to online of account id tAccount
end tell
if isOnline then
tell application "Adium" to disconnect (account id tAccount)
tell application "iChat" to activate
else
tell application "Adium" to connect (account id tAccount)
tell application "iChat" to quit
end if
end if
Basically, if the .Mac account in Adium is connected, it disconnects it and launches iChat, otherwise it connects it and quites iChat. Use Quicksilver to easily launch this when needed. You can use the above image as icon if you like.