Full Text Search is slow only for certain words

Hi all,
We have a Full Text Search setup on one of the tables in the SQL Server 2005 database.
It works fine for most of the cases, returns results in a matter of a second. But every once in a while, it times out in our application when searching for certain words. Does anyone know why some words take longer to search for than others?
For instance, searching for a string "Mike" takes 4 times as long than searching for "Jack".
Any ideas?
Regards
Narine

Check the following....
SQL Server 2005 Books Online (September 2007)
Performance Tuning and Optimization (Full-Text Search)
http://msdn.microsoft.com/en-us/library/ms142560(SQL.90).aspx