With Evolution 2.3.2, you can now compile plugins (based on the mailer) independent of the Evolution sources, thanks to NotZed. Building cool and nifty stuff so quickly with Evolution was never so easy as it is now. To confirm this, the Evolution community is planning a hackfest today at #evolution. More at the evolution wiki . Drop in and have fun.
And yes, I agree with Garnacho. We need to find some place to store all the wonderful plugins that are going to flood us 