GTK2 leaks a lot, but its realy depending on how many files you have in download, with 1-10files no big problem
with over 10 you proabably have to restart your amule once a day
but all this liked against gtk2!!
like skolnick said, with gtk1 its no problem at all....you can run your mule for days without having to worry about it

also with wxGTK2.5.4
btw: with 2.4.2 it would leak alot aswell with gtk2, even more then now with 2.5.4, but usually 2.4.2 is compiled with gtk1 so thats why there are no problems