What ID242 suggested is probably your best option with the current feature set in UBB 7.5.8.
The Google site search works great.
And it can co exist with the native search field
But it will take a while for google to crawl and index a large forum.
Then suggest to your users to use the google search field instead of the native search field.
But there has been talk of a cloud tag feature similar to what wordpress has available.
But it has not even made it to the consideration table as of yet.
