Dijkgraaf - 1:33 am on Sep 13, 2010 (gmt 0)

One thing to speeds things up is to use UNION ALL rather than just UNION if your database supports it.
If you just use UNION, it will try and remove any duplicates, and that creates extra overhead and hence takes longer.

However due to you doing a wild card search with your like '%keyword%', it isn't able to use indexes effectively and is probably having to do a full table scan of each table to try and find matching records.