Obviously the only options you will have on the advanced search page are:
Key Words:
Search In: Thread Titles/Posts
Sort Results by: Relevancy, Date Asc, Date Desc
Search in Forums:
And I guess searching by username will still be the built in way. (As in, without a search term, just list his posts.)
Gonna try to hack that up, when I make it work I'll release it I hope
But the fact you can index 4k posts/second is absolutely insane, and that was with 800 users online...