Brion Vibber
I've temporarily disabled the wiki's internal search engine on the English Wikipedia; searches are directed to google with a site-specific match.
If the search feature is slowing down the site, I think using Google would be a satisfactory permanent alternative. We've been using it for years at the PR Watch web site, with no complaints.
Google opened their APIs up for public use awhile ago. I haven't looked at them, but perhaps there's some way it could be used to lash together a search feature that would simultaneously search several Wikis all at once.