There is a search function to search all boards, but there are two problems with it.

1) I don't know of any short cut to reach it. The only way I know of to get to it is to go to "site map" at the bottom of the page then look for "search boards" right below "discussion boards."
That will bring you to this page which technically should search all boards.

http://www.theeroticreview.com/discussion_boards/searchMessages.asp

2) This is the bigger problem. It doesn't work. Takes you to an error page. I don't know if that is somehhing they are actually going to fix or not