Hi Wolfgang,
Are you still considering switching from CVS to a distributed version control system? The following is a pretty interesting summary of a few of them: http://www.livejournal.com/users/bramcohen/17319.html?thread=163751
I've dabbled with ARCH (tla) and monotone (only since the weekend) to pull the u-boot CVS into a local repository and merge/control local changes while tracking the master repository. After reading the above article, I've been reading up on DARC as well.
With ARCH, my approach was to create a Sourceforge CVS -> ARCH master, using ARCH to create changesets that tracked the Sourceforge CVS master repository. I then created a "local master" ARCH repository and applied the "master master" patchsets to the "local master". I've had some problems tracking the master repository successfully.
Monotone looks promising because Linus was considering using it and because, according to the article, git closely resembles it. If you're going to grab a tiger tail, might as well grab the tail of the biggest one ;-) Monotone is designed to make multiple branches and multiple heads easy to create and merge, which seems to be a good way to go for tracking a master and simultaneously controlling local changes. I don't have enough time in on it to see how well it works in practice.
DARC looks very promising for slaving off a master repository with local changes. I like the idea of being able to easily forward a changeset to the Repository Master (you), and then, when it gets accepted, undo the local changeset and apply the master changeset. ARCH can be used this way but DARC appears to be structured more for this type of usage with its emphasis on independent commutable patches. How well it works in practice remains to be seen...
Thanks, gvb