It always has with all forum versions.  

Simply due to the many many many posts that are searched.

If you restrict the search a little by date / location it tends to work a little better.

It is something I am looking into.

Should be a little better now.  It doesn't search inside [tags] as default now, which means the files do not need to be run through the YaBBC tag converter for each searched file.

This is one of the issues with the YaBB forum software - It does not use a dedicated MySQL type database (which is extremely fast and ideal for forum use), it uses a flat file system instead, which can be slow when trying to do large things.

The good thing with YaBB is that as it is a flat file system it is easy to maintain, ammend etc, and is less likely to suffer total data loss.