My problem with apropos (and man, for that matter) is related to how at least one major distribution handles the man pages. Rather than bundling the man pages with the applications, the man pages for many applications are bundled together in one base package. When this is done regardless of whether or not the application is actually on the system, apropos and man continually return information on applications which are not on the system.

"Google for manpages" as it's called... Especially helpful on a system without an internet connection :)

In my opinion it sucks. It is possible that I suck, but I almost never can find what I'm searching for with it.

Now I found that full text search is man -K, but it searches through sources so it can also be quite useless. Is there a desktop full text search for man pages? It should use rendered man pages. It could be a fun project. Google doesn't count and I use it already.