Additionally, if you're looking for an exact string in a search, adding quotation marks ("Term Here") around your search in conjunction with using site:bitcointalk.org will yield posts and threads on Bitcointalk with the exact string of words you have in the quotation marks. I've had very good results while searching with the quotation mark method, and I haven't ever used the forum's own search tool since I joined this forum- it's always been pretty crappy, and I doubt many people actually use it.
The forum also provides a link to Google search things on Bitcointalk
here (click here). I found this link while clicking on the magnifying glass next to the search bar on the forum itself, and it seems to work decently well, though I haven't personally used this before.