>is the NIO java technology included in the 3.5 series?

Nope. Converting to using the NIO classes is a huge undertaking.

>I've not found a decrease in memory consumption yet

3.5 doesn't have any large changes in memory consumption. Of course, we constantly are reviewing to speed up the slowest points in the code as well as trim down the largest memory abusers. Somewhat unfortunately, all the 'easy' ones have already been taken care of... so further changes will require some heavy sleuthing and changing.

FYI, there are also a few other notable changes with 3.5.1:
- Windows users (using the English version) now have the option to start LimeWire on system startup. This will significantly help the network, as well as improve the speed with which LimeWire starts when you want to use it -- it will pop up immediately and be ready for searching.
- Upload queueing logic is improved. LimeWire will now allow an upload if it notices that enough upload slots are available for a particular queued upload AND all of the uploads that are before it. This will reduce the amount of time that downloaders will have to 'wait in line' for a file, as well as increase the speed with which files can spread throughout the network.