This aroused my curiosity, sniffing the network traffic confirms the IDE does call home. It accesses the arduino.cc website server when first started. It doesn't appear to do anything untoward but requests a 'lastest.txt' file which contains the following :
HTTP/1.1 200 OK
Date: Wed, 29 Sep 2010 06:32:27 GMT
Server: Apache
Last-Modified: Sun, 10 Jan 2010 20:10:50 GMT
Accept-Ranges: bytes
Content-Length: 6
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Content-Type: text/plain
Can't find much else going on, in comparison to what many software packages do with an internet connection its extremely tame. This is version 0019, I'm running.