Be careful of calling memory usage a memory leak. But what exactly are you doing to cause this? I did some quick tests parsing a 40MB and 120MB log file(clearing encounters each time) and could only get 400MB of memory usage at best. ACT kept unallocating old memory when the GC deemed it necessary.
I also macroed my keyboard to iterate through all tables and graphs in memory, but I could not get memory usage to increase at all. So I have to ask... what
exactly are you doing?