no I've never considered it. I considered changing forum engine but I guess it would be a pain to transfer all the posts that's mainly why I stick with PhpBB. Indeed the search function is disappointing. I would say useless. I hope it will be improved somewhen. I never used it before I read your post. Since questions on this forum are categorized by FAQ people wouldn't need to use it so often either (fortunately). Maybe I'm gonna deactivate the search function.
Google doesn't really do a better job on your serach as you can see here
(you can change "music websites" to anything you want).
Unfortunately there aren't many music websites linked here (one? two?).
Also note that this is only only the forum of my website. My website is here (just in case):http://iwebfaq.org/site/iWeb_FAQ.html
There you will also find an FAQ about implementing Google search into an iWeb website to perform searches website-internally.
Regards and thank you for your post,