My colleague Dave Methvin jumped on the news about Microsoft's use of the jQuery library before I did, but it has to be said: it's something that says as much about the state of open source as it does about Microsoft. Most of it positive, actually.
This is one of many steps Microsoft needs to take to undo the damage it did to Web standards over the past decade-plus, and earn back some good will. Using and contributing back to an existing project in the above sphere (Web standards) rather than trying to go it alone and expecting everyone else to fall in line is a solid step in that direction.
The one thing that I do not see changing, however, is Microsoft's sense of animosity toward Linux. Microsoft may be softening its stance toward open source and making itself a friendlier player in that regard, but its stance toward Linux certainly hasn't softened.
What might happen -- and this would be all for the better -- is to have Microsoft cast that rivalry more in the terms of one platform vs. another. Make it more like the way Windows competes with the Mac, rather than it being one development or licensing model vs. another. And it doesn't even have to be because Microsoft is trying to be a nice guy. It's just easier to compete with something specific -- like Red Hat or MySQL -- than to compete with "open source" or "Linux" generally.
Still, congrats to the jQuery gang, and kudos to Microsoft for doing the non-evil thing. Heck, at this rate, if the next version of Office uses ODF by default, I might end up losing a bet.