The "u" shaped DID DirtStars were very tough my 04 had them and I never bent a rim over a very abusive 2 year period. My 06 has the new DirtStars with the traditional shaped rim and they have many dents and tweaks after one season of abuse. I do think the new versions are lighter, in turn sacrificing strength.
The other nice thing about the "U" shaped DirtStars was the mud didn't seem to collect on them as much as the traditional shaped rim.