At least using Opera or FF, you can just right-click any text input and create a search from it, so entering "php blah" in the address bar would search php.net for "blah". So yes, I use it on-site searches all the time. Why google for "foobar wikipedia" when I can just enter "wp foobar"? :)
I was doing the same until I realized that googling or binging (let's not rely on google too much) is most of the times faster than using php.net's own search engine. Plus, you're not limited to function names and you don't have to spell them correctly to find the right result.
Fair enough, but I still think that on-site search is desirable in general and many cases. I get that it's too much hassle for small sites, but for bigger ones, I wish they'd at least offer "bingle custom search" additional to their own. Completely outsourcing that is a step back to me, but then again I don't have to pay for the servers so I'll shut up now :D
