The search form requires you to input a keyword. The problem with this what if I want to search for, say, all posts by user X in forum Y. I can't seem to do that. I was going to post this as a bug, but was a little undecided, so here it is as a suggestion. Note that this refers to the Advanced Search form. The navbar search form allows you to search for all posts by one user, but you can't specify a forum.