Second bit.
The Log files you talk about I presume are Saved Chats
You still need to tick the box in Messages > Preferences > Messages that reads "Save History when Conversation is closed"
Old Saved Chat remain in ~/Documents/iChats (this was the default place and you may have Saved them somewhere else)
New saves are somewhat Hidden.
In the Finder use the Go Menu and hold the ALT key to see the Library option and then select the Library
Then Open Messages (A new folder in Lion if you used Messages Beta or in Mountain Lion)
In Archive are the Saved Chats (Compared to Messages Beta they are only saved if the option the the Preferences is ticked)
iMessages Saves seems to be in the chat.db item in the Messages folder itself (Some of it's function though is to bring up the "history" in an iMessages chat.
3:26 PM Friday; July 27, 2012
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Lion 10.7.2)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously