In February the Patent Office accepted a patent application from Microsoft patenting load balancing based on communicating about load between servers. The patent basically deals with the concept of having the load balancer server talk to the other servers to work out which one is best to give new data to. The patent dates from June 2003 where it was filed in the United States. It wasn't until a year later, in May 2004 that it was filed in New Zealand.
Any system which communicates load and status information in order to balance the load of incoming data could possibly infringe this patent. The big question is whether this kind of thing has been done before June 2003? If I were the CEO of a software company selling or using load balancing I would be worried. The good news is that organisations and individuals now have the opportunity to object. The patent is number 533148.