As you mentioned booting from a LUN is a great idea. Especially when you are running ESX on UCS blades with booting from a storage LUN, even if you have a blade failure, you just have to move the service profile to a different blade and your server is back up without involving your storage/SAN team to assign the LUN to different initiator WWPN.
As long as you have redundant SAN/Storage infrastructure, there is no real world problems as such with boot LUN. There could be certain application requirements which forces some customers to boot from local disk, but I am sure major portion of the servers are booted from SAN/iSCSI LUN in real world.
Initially we deployed ESXi on our B200 M3 blades with the USB key drive. Since then we acquired a block storage array and new ESXi hosts have been deployed with boot-from-SAN. No problems to speak off with BFS. I would be more hesitant with BFS for a physical Windows server.