I've found LinqPad so useful that I leave it open for days at a time, and it fairly quickly reaches significant memory usage, right now 850mb private. Closing a few tabs it goes down to 600mb private.
On startup for me it uses 130mb private.

I'm wonder what is preventing the memory from being freed, and what could I do to allow it to free some?
Perhaps you could add a small 'X' on the result set to be able to close that when I want to save the query in an open tab for a longer time? Or a option somewhere to dump all the compiled in memory assemblies?

Or have a little window that can be brought up to show the current usage of each tab... probably more work to show that than its worth really.