GitX is available at https://github.com/brotherbard/gitx/downloads (Get the experimental branch)
Git Tower is available at http://www.git-tower.com/
Textmate has a GIT Bundle at https://github.com/jcf/git-tmbundle (It's quite good, but maybe not for designers).
And Giggle (http://live.gnome.org/giggle).
Windows is the only OS lacking a good client, but I use GitX for Mac every day, as do the less technical "devs" at our Startup.
Git Extensions (http://sourceforge.net/projects/gitextensions/) is actually really, really, good. The UI is well-designed and fast. Wish more people knew about it.
I've been using the whatever default Windows port that is linked from Git's download page for several months bow and there is nothing atrocious about it. It works well and it does differ much from the Linux version. (edit) The command line version that is.
I use TortoiseHG and I expected parity.
Given that git was created for hosting the Linux kernel, it should be obvious why it's not a first-class citizen.
And of course, the command line option through msysgit is great.
Since the target group were designers, the presenter used a Mac, and tried to do everything using a GUI client for Git. I don't remember which one he used, but it ran natively on the Mac and it looked quite nice.
(Still, the presenter sometimes struggled with that GUI. He was obviously more used to the command line.)
I use Git, and its a wonderful piece of software craft indeed, but it does not have Windows/Mac clients, that designers often use, as their base OS.
A decent usable frontend for Git, on platforms other than Linux too, needs to be developed, for it to be usable by designers.
Edit - I meant to say officially supported frontend and support for other oses by git.