The newest information on it that I came across was right in the book The Herpetoculture of Leopard Geckos. That book has several very interesting studies in it that tend to contradict, at least to some extent, things you are told online. I'll have to look for online links where I had read about it before. I know a couple were Zoology type sites.
It is true, in captivity many Leos do not do well with others. One big difference is probably the limited space they are given to co-habitate in, as compared to in the wild. Of course this is especially true of males. But, it has been shown that 2 males raised together from the time they are very young can continue to tolerate one another as adults, as long as a female is never introduced. Now, I said "can" not "will" LOL I definately would never recommend it.