Almost all git vs mercurial differences for most users are cosmetic/usability/culture related. With a few extensions turned on, you can use either interchangably. The biggest exception to this is if you use named branches (a fairly common thing in git, slightly less so in mercurial). Mercurial hard codes a branch name in the metadata of a commit, git doesn't do that. I prefer git's method as it means that a commit can move around on branches (or really that branches can point to different commits) without messing with the commits themselves.
Branching is one of the big differences. I find Mercurial's named branches mostly useless; fortunately, with some care, bookmarks can be used to simulate Git-style branches.
I think, early on, the Mercurial community favored cloning as the means of creating feature branches, while Git used named branches to do so. But in many cases you want to be able to switch lines of development in a single repository (especially when using a workspace-based IDE like Eclipse), so the Git model becomes a win.
