I think the way most any Gnutella app thrashes the winsock you're likely to have problems after several days running. Gnutella is just very, very resource intensive due to all the connections it goes through.

Another possibility is Gnucleus keeps a lists of things like failed uploads/downloads etc. I don't know if there's any limit to the size they can grow, and they must take memory. I know they can grow so big as to really overload the list box when you try and display them.