There is no way to limit the RAM. There are no big memory leaks I know of, but for example if you don't clear completed uploads/downloads automatically, if you do lot's of searches etc. it's to be expected. Maybe there's also a problem with the Java's garbage collector on MacOS.

__________________
Morgens ess ich Cornflakes und abends ess ich Brot
Und wenn ich lang genug gelebt hab, dann sterb ich und bin tot

--Fischmob