Which do you mean? Git-GUI is not "very nice" by any means. TortoiseGit is decent but a new Git user is hardly guided there (compare that to: http://mercurial.selenic.com/downloads/).

Also, my point wasn't specifically about GUIs per se but about usability overall. Git developers have only very recently, and only very grudgingly it seems, accepted that usability is even a serious concern. Considering that a developer will have an enormous amount of interaction with source control tools (almost as much as with an IDE or build tools in general) usability is obviously a huge factor. Git has a lot of the technical aspects nailed but I would be shocked if it won the current battle for revision control system of the future.