I was having this problem before, trying to search for topics I remembered seeing earlier, but thought I wasn't being systematic enough. Now I don't know what is happening.
Example: I posted a topic titled "ISO great food in Santa Barbara for casually dressed travelers" on the California board. Checking back later, I couldn't find it at first. When I search for "Santa Barbara" or "travelers" or "ISO" or "great food" my post does not appear among the search results. When I search for my name or "casually" or "dressed", it does. Huh?