Over the last week, the VPS serving my sites started getting out-of-memory errors. Instead of debugging while processes fail to start (never fun), I got out my chainsaw and cut down the biggest memory hog, apache2.
Everything is now running on lighttpd as CGI or fast-cgi. I've tested the heavily used sites and they're working fine. The infrequently used stuff may not be as I've not tested it yet. For now, though, I have some breathing room in which to find and profile the memory spiker.