PHP is very good for little, dirty projects coded in a weekend, but also for big, long-running projects (well, maybe Java and Rails are better for that).
Facebook, Yahoo! and lately (at least, looks like) twitter (that's just a guess after seeing their server-status pages) do use PHP. I do, also.
You can build huge projects using a self-made (or external maintained) abstraction structure fitting your needs (database, data clustering, middleware). Or just a countdown page with the days before the next party (?). And, in both examples, it wouldn't be slower to code things with PHP than with RoR.
Facebook, Yahoo! and lately (at least, looks like) twitter (that's just a guess after seeing their server-status pages) do use PHP. I do, also.
You can build huge projects using a self-made (or external maintained) abstraction structure fitting your needs (database, data clustering, middleware). Or just a countdown page with the days before the next party (?). And, in both examples, it wouldn't be slower to code things with PHP than with RoR.