I ran into two problems when using Chat Transcript Manager for the first time. When I selected chats within the last week, it showed me nothing, even though the chats existed. When I selected "Last 3 Months", CTM locked up with the spinning beachball while it scanned my iChat transcripts. After a force-quit and relaunch, CTM worked fine.
The interface is very useable and attractive. You can customize the chat transcript display with its NetNewsWire-like "styles" feature.
The "Chat Contains" filter is a neat idea. It makes it easier to find out when you sent a picture or a web link to a friend.
If you want a chat log program that looks great and has plenty of features, this is the one. Despite minor glitches, it's a solid program.
My own needs are simple so I'm sticking with Logorrhea. It doesn't have as many features, and it only supports iChat, but it's free. It's been around for years and it's very stable.