I've just finished writing a new plugin for XenForo that displays your last played game next to all posts on the forums. Currently it covers PSN and Xbox Live. I'll add Steam support later.
The data is displayed in the user info bit, as shown above. It retrieves data automatically based on the information filled out in your forum profile and is integrated with the gamercard system, so any updates will be in sync. Also, we use the timestamps direct from PSN / XBL to determine what game and platform to show so the info should be accurate. Enjoy
PS: Due to some DB changes I had to rebuild our cache, so not everyone's info may show up yet. The rebuilding process will take a few hours at most.