Cumulative Update 1 for SQL 2008 RTM contains fixes for two nasty FILESTREAM bugs (among a lot of other bug fixes).
The first one concerns restoring a 2008 database from a series of log backups when the database contains FILESTREAM info. It's possible that a race condition can cause one of the log backups to miss backing up a FILESTREAM file – resulting in a corrupt database after a restore operation. See KB 957809 for more details.
The second bug occurs when a clustered index is rebuilt using ALTER INDEX … REBUILD and the table contains FILESTREAM data. In this case, it's possible that all the FILESTREAM files are copied, meaning the rebuild operation can take a very long time if there's lots of large FILESTREAM data values in the table. There's no need for the FILESTREAM data to be copied during an index rebuild as the FILESTREAM locations and filenames remain the same. See KB 957823 for more details.
You can get the fixes for these in CU1 – see KB 956717 for the download (right at the top of the page) and the list of all other fixes included in the update.