As a matter of fact, I did a Google search yesterday on a user's name. It was somewhat effective, but I think I only found about 150 of the poster's 600 messages. It helps if the user has a particularly unique user name.
The google domain search IS somewhat helpful for finding people's posts, as bicker confirmed. Unfortunately, though -- unless I don't know a trick that's available -- I don't see any rhyme or reason to the results listed. The first several posts I found from a user were from 2000, 2006, 2005 and then finally 2007.
I pointed out in another thread that if you want to find old DIS posts, Yahoo is far better than Google. See thread:
http://www.disboards.com/showthread.php?t=1085825
I had been trying to get the search by username function to work here on DIS with no success, so I went browsing the DIS tech support board, and there I learned you can go to Google and simply type in the user name you're searching for followed by site:disboards.com. I tried it, and was impressed.... until I tried it using Yahoo.
Google: 44 of my old DIS posts
Yahoo: 184 of my old DIS posts
So then I tried another user, "Trentmom". (I was impressed by her 6,700 post count within 5 months of registering!!).
Google: 821 posts
Yahoo: 2,960 posts!!
Try it on yours, see which one yields better results...

Tonight it's working again. I'm still hoping for an update though, Board Tracker. How close are we to a fully functional and consistent search option? Thank you!