We decided to use DNS Round Robin to "load balance" our Windchill cluster when we went live about 2 years ago. We understood the risks in that it's not supported by PTC Tech Support but management decided that it was worth it in light of the expense of true hardware based load balancers. That being said, we are experiencing an issue now with testing IE 8 that we believe is directly related to the use of DNS RR and the users' session affinity not being maintained.
How are you guys handling your load balancing for those of you who have clusters? Do you use hardware based devices or DNS RR?