The most popular & well known Physics Engine (PhysX) going Open Source....of course it is.
Nvidia doesn't normally have Proprietary stuff go open source - so yeah, it's a big deal.
Probably really going to help w/ AI, robotics, and vehicles here - since NVidia already is getting their stuff everywhere in those departments.
Now, also - anyone can use the code and make stuff w/ it.
Also, this could really help older games that actually (for some reason) required PhysX package installations (think GR:AW games, ME2, Sacred 2, and Velvet Assassin come to mind - there are others). Doesn't effect Nvidia users too much (easy enough to install Legacy PhysX drivers, if you are an Nvidia user), but this is especially important for those who did not utilize Nvidia products - i.e. any AMD users. Now, if someone wants, they can take the Open Source from PhysX, mod the PhysX code and files if need me, mod the game, and make 'em work much easier - let the mod out and we're good to go.
Otherwise, like it has been before this open source announcement - one would have to install NVidia's Legacy PhysX software package or the old AEGIA PhysX package; or find the files needed to make this crap work & mod it that way...hopefully. Cross your fingers that it works.
Always nice to see Propriety software and any games go Open Source at some point - especially if they're trying to keep software and/or games alive and preserved, lots of years down the road.