On both systems, you can't do anything but search for the first instance of a message. It is completely and utterly useless. It also hangs and and crashes on my system if you try.
ED: I tried searching for a word in Messages at five minutes ago, and the results still haven't appeared. 100% CPU usage.
ED2: 10 minutes now, 2.24GB of memory use.
ED3: Results showed, then client crashed at 13 minutes.