One thing I'm all for is the world of open on the web. I can't be bothered with registering, subscribing and paying. Surely the whole point of the net is to have everything at your fingertips? Who wants to jump through all those hoops?
I'm a big fan of FileHippo. Many of the programs I've downloaded are open source. I'm not crazy about the whole open source movement (I take a practical approach rather than an ideological one), but I fully support anything to do with open source and open data. With freedom of information, it makes it a whole lot more practical to make everything available online instead of spending hundreds of man hours working through request after request. Not to mention the advantages of creating RDF schemas for such data and creating huge mashups of information.
On a personal level, open source comes a lot into my everyday life creating for the Sims. There is a big divide in the community about being 'fileshare friendly', or choosing to withhold or charge for the content you have created. This goes not only for custom items, skins and objects, but also for custom programs made to get the most out of the game. It is a very contentious issue, and still divides the community after many years. It seems that open source is something that people feel strongly about on both sides of the divide.
Sharing my creations freely is, for me, being part of an online community to get the best out of your game. Also, the ability to push the boundaries with your creations and 'show off' what you can achieve is also a big motivation. It is also a great way for creators and users to share their ideas and needs, to look outside the box and to create things from a whole new viewpoint. Creators create in response to other player's needs as well as their own. This makes the community atmosphere very productive, stimulating and open-minded. And more often than not, people are passionate enough about a service to donate in order to cover costs, so it works both ways.