There's an article on Download Aborted proposing that the producers of Shrek should use distributed rendering screensavers to save money on the renders of Shrek 3.
It's an interesting idea, but I suspect that it's suffering from a failure of imagination. On the one hand, cycles are cheap and getting cheaper -- yes, CGI is processor-hungry and that hunger is ballooning, but CPUs are ballooning faster still. I expect that in the medium-term, the rendering expense will be paltry as compared to custom code development, artists and especially marketing. If you're starting with a couple hundred mil in budget, dropping one, two or even five percent on a bunch of white-box PCs is just not that big a deal.
Now, indie filmmakers, students, and garage auteurs, OTOH, really can't afford the cycles to render a cinematic quality CGI film. These are the kinds of people a SHREK@HOME screensaver could really serve, and if you made it social, it could do double-duty.
Ultimately, the largest expense in an Internet marketplace where anything is available always anywhere is marketing: the more choice, the more expensive influencing choice becomes.
So a social SHREK@HOME could engage its audience not just for their cycles, but for their evangelism. We see glimmers of that in some machinima projects, like Red v Blue or in Flash-shorts like Homestar Runner, a clubbish sense of ownership by its fans that turn them into relentless marketers of the net-art.
The more engaged fans are with work, the purer the evangelism (hence the blogging bore and every other otaku who can run on about her hobby forever). It's hard to be really engaged in the creative process of "shooting" CGI -- I don't know enough about 3D animation or visual art to second-guess those who do. But there are ways that even the unskilled can contribute.
Imagine a distributed renderer that included along the bottom thumbnails of alternate test-renders of the current sequence: different lighting, camera, even new inverse-kinematics and chaining. These different sequences could be created by the filmmaker and/or by more knowledgeable fans. While I render out the authoritative version, I can click on any of these little animated thumbnails and devote an equal number of cycles to rendering it, producing, in effect, an "audience cut" of the movie that can be matched with the foley and ADR in post to allow for different views on the same flick.
On top of that, layer the useful bits MMOs: guilds, pledges, fan-sites, etc. Create affinity communities around different edits and renders. The more excitement you build for your movie, the more cycles end up being devoted to its production: the more cycles, the more variable renders and the more excitement.
The software is pretty do-able, it's the kind of thing Nelson and Marc were doing at Popular Power and Adam "distributed.net" Beberg was talking about with COSM years ago. The legal apparatus might be harder, but a CC-license could take care of that.
The result would be ten million times more exciting than the mundane process of donating some of your cycles to Shrek 3 -- it would be the basis for an entirely new way of financing and executing film production.