For the most part, there is a slight increase with 6, especially while performing an upgrade. Otherwise it should be the same as previous DNN versions.
Does your memory footprint include SQL server? 100 MB should work with extra effort, 250-500 MB is a reasonable trade off, although you may need 2-4 GB to run DNN and SQL server on the same machine.
There is alot of background activity that goes on in DNN, especially event logging, indexing and individual module activity. Add vistor tracking and caching to the traffic and it becomes a science. The difficult part is to determine where the extra RAM being used.
http://www.dotnetnuke.com/Resources/F...
http://www.dotnetnuke.com/Resources/F...
I hope this is of some help to you.