When I close the IDE window, the closing process take unusually long time (10+ seconds). I have the latest IDE version, Windows Vista, dual core processor, 2GB RAM. Why is it so slow? My project is quite large using Doctrine and Zend Framework. Switching projects is not so slow.

Please check that the disk where you store project (ppj) files is fast enough. Upon shutdown the IDE saves code insight database on to the same location with ppj file and it may take some seconds if drive is slow (for example remote or flash drives are usually slow).