A possible cause for this behaviour is that the journaling file system of the NAS system slows down the processes of SDL Trados Studio. The significant changes in handling translation memory data in SDL Trados Studio 2011 seem to collide with the journaling file system feature.
A description of the journaling file system can be found here on
http://en.wikipedia.org/wiki/Journaling_file_system and
http://de.wikipedia.org/wiki/Journaling-Dateisystem. The latter is in German, but includes more information and can be simply translated with SDL Freetranslation.