This article reminds me of a quote from a Bruce Sterling lecture: http://uscpublicdiplomacy.com/index.php/events/events_detail...

"Hackers love IP. I mean, Eben Moglen, I saw this guy. He says, you know, we're not going to be able to convince the ruling class to change things the way we GNU freaks like it, so let's just make it really complicated! Just go in there and hack the living daylights out of intellectual property! Just quibble, quibble, quibble! Raise hell! NIMBYize all the time! Until people just become critically bored with it, and they just throw up their hands, because I just can't be bothered. I can't keep track of all my licenses, and my this, and my that, and the other, and it's just completely unmanageable."

If I release an open-source project with a logo of a little horse, and don't trademark the horse, then someone else can use that horse, completely separately from my project, to represent another project that has nothing to do with mine, and thus dilute my project's brand. Is there any way to reduce the impact of this without closing the source to the artwork?

To clarify: (1) Your scenario = don't trademark, use open source license. (2) What Mozilla does = trademark, use proprietary license. (3) What Mark thinks should be done (afaiu) = trademark, use open source license.

I don't know a good way to reduce the impact in scenario (1) through legal means, but if you are worried about this, why not choose scenario (3)?

I think you're supposed to trust the commons. The commons can do no wrong.