And yes, I've tried both Ubuntu 12.04 and OS X 10.8 for several days as my only work-based machine to road test both properly.
The truth is, Unity sucks. A lot. Even after you get used to it. It was a poor decision by a set of developers out of touch with reality or their user-base, and it's only beginning to recover and move in the right direction slowly.
Everyone I know is migrating to Mint and Xfce/KDE4/Cinnamon (Gnome 3 fork), and with good reason.
OSX is still way ahead of the curve, but Linux (not necessarily only Ubuntu) still has a chance. The idea of Linux is still great: we're hackers, so if you feel there's a problem, help fix it. Not easy, but the fact that you can is pretty cool.
I know that's off-topic, but I really think everyone/thing Ubuntu related should be focusing on the fact that the desktop doesn't cut it, the OA is off-topic if you like. When you write software, you write it first, properly, then worry about optimization when it's functional (with a few exceptions). If it doesn't do its job, who cares that it can unzip twice as fast.
So, the problem with this is that what you think is important might not be what other Ubuntu users think is important.
Also, I've installed Ubuntu 12.04 on my MacBook Pro, and it _just worked_ (TM) out of the box.
"If it doesn't do its job, who cares that it can unzip twice as fast."
Unless of course you're day to day work involves unzipping large amounts of data, in which case it ends up being important.
Not that Ubuntu/Unity fares better in that department, but right now, all the major players aren't really doing a swell job with their desktops.
In any case at least GNU/Linux distros can easily be customized to fit one's needs. That's an important factor in the software usability metric that is often forgotten.
Also there's more and better and easier access to Unix tools on Ubuntu, just about everything is an apt-get install away. I've used third party package systems for OS X but it looks like there's no clear winner among them at least last time I looked, and some software just isn't available in recent versions without compiling or troublshooting it yourself, which I find to be a big waste of time. YMMV.