I would imagine there are still a reasonable number of platforms for which darcs doesn't exist yet.
As someone who follows along in the development of Slime -- and someone who gets regular updates via CVS -- I can say that I wouldn't
fyi, seems like i was the only one pushing it, but i already gave up. i'll keep my branch in a publically available darcs repo, though.
darcs binaries: http://darcs.net/DarcsWiki/CategoryBinaries