Heck no. Check out the hgsubversion plugin for HG. It is getting pretty close to seamlessly hiding SVN as a parent of an HG clone. I've been using it for a few months on a large project (ca. 450k LOC, 8 years of history). You "hg clone svn+http://..." and then you can hg pull/push like normal. I haven't tried any major cross-branch merging -- I still do that in SVN at the moment -- but it works really well. I've got an HG SVN clone on my desktop at work, and a clone of that on my laptop.
I don't know about the HG/CVS possibilities, but I wouldn't be worried about DVCSes.
And, on an unrelated note, I'm really happy about Google's decision. I evaluated git a while ago, and I found it kludgy and awkward. A revision control system should stay out of my way and be a useful tool, not become a full-time job with an equivalent learning curve.
I don't know about the HG/CVS possibilities, but I wouldn't be worried about DVCSes.
And, on an unrelated note, I'm really happy about Google's decision. I evaluated git a while ago, and I found it kludgy and awkward. A revision control system should stay out of my way and be a useful tool, not become a full-time job with an equivalent learning curve.