Me and my girl have had a threesome with another girl before (my girl likes the ladies too lol) and we both found it to be great, hell my girl was having sex with me like a rabbit for weeks afterwards. I guess it all depends on the couple; like if its just the guy wanting to do it (or the girl) then there will be problems but if its a mutual thing it really can be great fun. Crazy people need not try this because there will be problems lol.