Membership and status would be easy: are they forwarding random packets to me? Then they're up and running. New computer sends packets? New service member, so tell them about members you know of. This would also allow multiple public ingress points (like running multiple simple load balancers) so clients could change which computer they send to, and bandwidth would be ~balanced.
I've never seen an architecture diagram for a high availability horizontally scalable system that included a generic load balancer.
When I give system design interviews, it's a bad sign of the interviewee adds a balancer. It ends up being a hand-wavy solution to difficulties on either side of the balancer.
+---------+
+--------+ |expensive| +------------------+
|internet+-------+ load +--------+a bunch of servers|
+--------+ |balancer | +------------------+
+---------+[1] http://www.austintek.com/LVS/LVS-HOWTO/HOWTO/LVS-HOWTO.UDP.h...