I have a Server with to uplinks into the Internet. I'm doing load balancing over both uplinks with ip utility from the iproute2 package.
~ # ip route show [...] default nexthop via 188.8.131.52 dev ppp0 weight 50 nexthop via 192.168.178.1 dev eth2 weight 50
If the server is under heavy traffic load then persistent connections like ssh or dowloads are simply dropped after some time. If I disable load balancing everything works fine, even under heavy load conditions.