Size of TempDB Microsoft SQL Server 2005
Tempdb will be recreated if the server is restarted and at that time tempdb will be reset size wise to initial size settings. In the meantime once the temporary tables are dropped space will free in the data files but size on disk will remain the same.

I wouldn't however worry about the size unless you have space issues.  Next time you run queries that use tempdb a lot you will save on growth operations and get a bit of a boost to performance since it will use the above mentioned free space in the data files