As you may or may not have discovered already, PBwiki has bizarrely decided to limit search results to 10 hits. That renders the search engine useless.
The solution I found to this problem was to use the FreeeFind Search Engine service. It has the great advantage of offering lots of search parameters, including wild cards, Boolean searching, and an "advanced search" form.
There is something VERY important you have to do in order to make this work, however. In order to exclude the multiple versions of pages, you need to go into to "Build Index" page and customize your indexing in order to exclude these pages:
*2007* (to exclude all the versioning pages created in 2007)
*raw* (to exclude all the raw HTML files which are also an "invisible" part of your PBwiki)
The other trick is how to get people to the Search engine you have built, rather than the crippled PBwiki search. What I did was to create a special Search page at the wiki, and then add a link to both of the Sidebar tabs, so that people will be able to see the link prominently on every page of the wiki. It's not ideal, but it's the best I could come up with!
If people have other comments and ideas about this, there is a PBwiki forum dedicated to the sad PBwiki search feature; let's carry on the discussion there and share ideas for work-around solutions!