I started using DCVSes with darcs and liked it quite a bit — a real breath of fresh air compared to the nastiness of cvs and svn. Nice UI overall. Unfortunately

I started using DCVSes with darcs and liked it quite a bit — a real breath of fresh air compared to the nastiness of cvs and svn. Nice UI overall. Unfortunately, it had a nasty bug where commits or merges would hang indefinitely. It was a hole in the theory of patches, I believe. The bug took forever to fix (over a year, if memory serves), and darcs lost momentum to Git, which worked much faster and more reliably (and has extra really nice features like the svn bridge).