...
Note: please sign your comments. Otherwise it may appear that you're speaking in an 'official' capacity for the SpamAssassin project, which is not likely to be the case.
Suggestion
I would suggest that the contest be done in a two-phase style. The developers should pick 2 or 3 of their favorites and then ask the designers for a final version. This will allow a designer to put the required effort to make a real logo, most of the ones in there still look like drafts.
It takes a lot of work to get things proper and I believe many of the contestants, including myself, would be more prone to put more work if you know that your idea is being seen as a real option.
And even then, once the finalist is chosen I would suggest that the developers and the designer work together for a while to really get it the way they want. This interative process is what's usually done in a professional setting I don't see why not follow it here.
(ChristianRauh)
Comments on specific submissions
...