[nikcub]

Expensive commercial appliances like the popular f5 big ip's can, and that is what a lot of large-scale websites use:

http://www.f5.com/glossary/load-balancer/

In terms of open source, HAProxy has layer 7 algorithms but they are much simpler:

http://cbonte.github.com/haproxy-dconv/configuration-1.5.htm...

If you were inclined, you could write an algorithm to implement something similar in one of the open source routers.