The current search function is completely useless.

board page, that will get extremely old posts, but it's pretty much hit and miss. Can be hit and miss with newer posts, too. But that's Google.

Advanced Search, which is for Star members only, is DU's own search and will pick up old posts by keyword quite well, but it's limited to searching for only one keyword (you can type in more but it'll search only for the first one, in my experience using it anyway). It works best for searching smaller forums. On a huge forum like GD you'll often have to narrow the time range for a search or it will time out.

a board like this.

Anyway, glad I could help!