Perhaps some context for what follows is in order. I'm an Ubuntu person who spends most of his time working upstream in GNOME. I do this because I think my work can benefit the wider community as well as Ubuntu users (and, erm, because I enjoy working on GNOME). It can be a bit crappy sometimes, though.
For starters, some  people in the GNOME community moan about how Ubuntu doesn't pull its weight upstream. They then make it difficult for Ubuntu-y folks to contribute things upstream. People within the Ubuntu community, Canonical employees included, have tried to make significant contributions and have been knocked back on several occasions , in most cases not for any particularly good reason I would judge. I've even heard stories about Canonical having to upstream patches via a third party because a GNOME maintainer wouldn't accept (identical) patches from them! (I know; citation needed.) There is an anti-Ubuntu (or at least anti-Canonical ) sentiment in parts of the GNOME community.
Equally, there is a frustration with GNOME in some quarters of the Ubuntu community. Rather than joining in on the GNOME side of things and developing upstream, people see the processes and dynamics of GNOME as hurdles to doing what they want to do. It seems easier to go off and partially reinvent the wheel than to try working with people who don't share your exact vision of the free desktop . Of course, there is no middle ground to be had, and the "irreconcilable differences" which prevent us from working together on one thing or another often lead to "completely different" approaches being taken, like Unity and GNOME Shell . This way of doing things is often a gigantic waste of time and reinforces the opinion of some in GNOME that Ubuntu isn't a team player.
To round-off this sketchy analysis of a complicated situation, I should also mention Canonical's role in all of this. Canonical are a for-profit company and intend to make money from the Free desktop. On paper at least, I think most people in the GNOME (and Ubuntu) community are happy for people to make money from Free software. The method you use to make that money is subject to intense scrutiny, however. Free software companies are already at a disadvantage compared to proprietary software businesses when it comes to making money , and insisting that all of their attempts to generate revenue fit into some warm, fuzzy picture of a benevolent cooperative for whom profit is incidental is unreasonable . Sorry folks, but it's the 21st century - even charities are getting cutthroat when it comes to fundraising, because they realise you can do more good by playing the capitalism game whilst remembering to stop short of the excesses of Big Business.
If you want the Free desktop to be successful, to gain significant market share, to compete with some of the biggest, most ruthless companies in existence, you're going to have to throw away some of your ideas about how this should work in an ideal world and start playing hard ball. I think this is what Canonical are trying to do. And yes, that involves exploiting  the community to some extent, and of course people are upset about that. I don't think Canonical are hell-bent on milking FOSS for all it's worth, but they do require some freedom to operate. Having said that, if Canonical want to push the view that a pragmatic, corporate approach to Open Source is the route to success, then they're going to have to do a lot better at not making people feel used. Things like splitting Banshee's Amazon referrals and insisting on copyright assignment cause bad feeling without bringing in much dough, I would imagine.
My point is that the bulk of this bickering is counter-productive and unnecessary. Open source desktops are hardly swimming in market share, and I doubt chronic infighting will remedy that situation. I don't care who started it, or who is in the wrong. From my point of view, the whole situation is depressing and demoralising. If it continues, chances are I won't want to work in either community. But the differences are reconcilable! GNOME can understand and facilitate Canonical's commercial goals and can be more accepting of Ubuntu people and their way of doing things; Canonical can benefit from the fruits of the Ubuntu and GNOME communities' labour in a more sensitive way; and Ubuntu contributors can resolve to work upstream more. All it will require is for some people to swallow their pride and/or make small compromises .
1 In a Darth Vader mask. Really. There are photos somewhere.
2 I would like to draw your attention to my careful use of the word "some" throughout this post.
3 I'm thinking of things like Zeitgeist, app indicators (which are a Free Desktop standard!) and so on.
4 I fully understand that Ubuntu and Canonical aren't the same thing, and that there are tensions between them. They often get tarred with the same brush upstream, though.
5 The decision to switch to Unity instead of GNOME Shell is symptomatic of this. I asked Mark about that decision and he said that attempts were made to get Canonical design people working with GNOME design people etc. etc. and no agreement could be reached. Despite this fundamental disagreement between the two camps, Unity and GNOME Shell are doing a great job of looking and feeling almost identical to one another.
6 Sorry to harp on about it, but GNOME Shell and Unity are extremely similar, to the point where hardly any of the differences offer tangible benefits to the end user. Helpfully, they're just different enough to cause massive problems for documentation and support people though. Working together on one new shell would have been possible on purely technical grounds.
7 By this, I mean that factors like the code being open mean that it can be more difficult to get users to pay up; revenue streams other than the obvious, directly selling the software, must be found. Of course, Free software has plenty of advantages in terms of reduced development costs, community contribution and the like.
8 To pick an example at random: "I thought you understood the spirit of Free Software, but you're just another normal company that is first going after money."
9 An ugly word, but I think it's the right one. You're making money by taking other peoples' work and packaging it up, without offering them any reward for that work (monetary reward, at least).
10 I will be swallowing some of my pride by working on documentation for Unity and assigning the copyright to Canonical.