For me, the built-in search function, accessible from the "SEARCH" link on the bar near the top of each page, doesn't work very well, and is slow. There are two other choices, on the home page: https://secure.thementalmilitia.com/
1) ixquick site search
2) Google site search
I have very little experience with ixquick. It was added for people who don't like Google.
Google site search works well for me. And it's nearly instantaneous.
Tahn L. is correct that the posts of members who delete their accounts on the way out are still there, unless they have "flounced off". Neither Mr. Bill nor Clip Johnson removed their posts when they deleted their accounts, but it sure is inconvenient to be without a listing of all of their posts, as provided by their now-deleted profile pages.
It is possible to restore a deleted account, using the account information from database backups, and some MySQL wizardry, but I won't do it unless requested by a member wishing to rejoin the forums.