We were using Pound for load balancing at Justin.tv until today. It was consistently using about 20% CPU, and during spikes would use up to 80% CPU. Under extremely high load, it would occasionally freak out and break.

We just switched to Ngnix, and load immediately dropped to around 3% CPU. Our pages feel a little snappier, although that might be my imagination. Not only is the config format easier to understand and better documented, but it offers a full webserver's complement of functionality. We haven't hit any spikes yet, but given the current performance I suspect it will cream pound.

In short: Pound is out-dated. Nginx is a good replacement, although there are many, many, many other options I haven't tried.

Nginx vs. Pound

Edit: More data now available!

Week view on Pound vs. Ngnix