Version control through the ages

It just occurred to me that over the past six or seven years I have gone from using CVS to track all my code and projects to using Subversion and from there to using Darcs. In general I find that each one has really been an improvement over the previous tool. I miss certain Subversion features in Darcs (specifically svn:externals) and get a bit confused sometimes when dealing with multiple repositories but the extra functionality is well worth the effort to learn.