LimeWire will usually need about 80mb on a Mac. If you have like a hundred active downloads or even more, that value will go up, of course. - IIRC there is also a little memory leak left in the current version, that would cause LimeWire to use lot's of memory if you continuously started lot's of downloads and killed them again.

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

--Fischmob