In a past life in the mid/late 2000s, I did 10GbE NIC drivers for a small IHV. VMWare was by far the most awful vendor to deal with. They had mandatory certification testing which was required to distribute the driver. Their tests were so much worse than MS WHQL. There was invariably something broken in their tests that we had to work around. Each time this happened, we had to go through their support (And pay for the privilege) to tell them their tests were broken and to give them patches to fix it. This would happen pretty much every driver release, and we would end up dealing with a different person each time.

My favorite thing about leaving that job was never having to deal with VMWare ever again.