Well, I'm been using Ageia PhysX in my current game engine, and it's fairly easy to use, easy to install, very very fast, well documented, and supports many features you'd only dream of in open-source physics engines. I've only used a fraction of all of it's features so far, but as far as I can tell my only complaint is that the character controller was somewhat confusing to get working right.
It's basically a $50,000 physics engine that was released for free a while ago. All you have to do to get it is register at Ageia (free, no obligations), and you're licensed to use it in anything you want (commercial or personal).
The only limitation is that it's Windows only currently, and you have to include a 30 MB driver with your game which includes every version ever released of the SDK DLLs. It will work if you include just one version with your game (about 3MB), but I think the license doesn't allow you to separate the DLLs like that, so your choices are to either include all 30 MB in your installer, or make the user download it themselves from Ageia.
It's basically a $50,000 physics engine that was released for free a while ago. All you have to do to get it is register at Ageia (free, no obligations), and you're licensed to use it in anything you want (commercial or personal).
The only limitation is that it's Windows only currently, and you have to include a 30 MB driver with your game which includes every version ever released of the SDK DLLs. It will work if you include just one version with your game (about 3MB), but I think the license doesn't allow you to separate the DLLs like that, so your choices are to either include all 30 MB in your installer, or make the user download it themselves from Ageia.