I've noticed that when I have my account sync setting turned off, and the background data turned off, that my Droid still downloads approximately 250mb per day in data.
The only connections according to OS Monitor are to the 1e100 (google) servers, and to some server called 'red.bizratepro.net'. I haven't been able to find any info at all on that last one.
Latitude of *off*, btw. I'm running AdamZ's Smoked Glass v6.01.