While it seems like everyone and their mother is licensing Epic's Unreal Engine 3, some developers are doing just fine with homegrown engines. GRIN is getting the most out of its Diesel Engine, with the recently released Wanted: Weapons of Fate, as well as upcoming games like Terminator: Salvation and Bionic Commando. However, the company doesn't recommend going that route. In classic example of "do as I say, not as I do", GRIN director Ulf Andersson told Gamasutra:

In the current economic climate, most developers aren't willing to risk the time and money on a homegrown engine, so Andersson's comments are certainly understandable. Still, I found it rather amusing that he said something to the effect of "we're lucky that our engine is so awesome" only to temper it with "don't try this at home".

Source