Good that we are starting to put concrete examples:

http://ubuntuforums.org/
Good reference but there are some deep differences that need to be taken into account when comparing.

- Ubuntu users are first Ubuntu users, and then users of whatever hardware Ubuntu is installed. Most of them installed the OS themselves in a piece of hardware that came with another OS. This means that they are well aware of the difference between OS and device, and they have a clear priority over the OS and the apps available for Ubuntu. MeeGo will be also installed in e.g. netbooks, but it is expected that the majority of users will reach first a device that comes with MeeGo pre-installed. This also means that the possibility of getting MeeGo vendors interested in own user communities is higher than the same possibility for Ubuntu vendors, simply because there are not that many.

- The Ubuntu experience is mostly the same across devices. Some drivers here, some branding there but once things are setup Ubuntu is the basically same Ubuntu everywhere and everybody polls from the same repos. Now compare the situation with MeeGo, offering 5 UX references and (most important) the possibility of having vendor specific repositories. Ubuntu apps are available for everybody but what about the apps pre-installed in a Nokia MeeGo device? Many of them probably not available for non-Nokia devices.

- The software in Ubuntu repositories is mostly free as in freedom and in beer. Alright, some non-free as in freedom but still gratis and freely downloadable. The commercial software aspect around Ubuntu is minor, if not negligible. This is a situation very different from MeeGo, that being an open source platform needs to be successful attracting commercial apps that again might or might not be available across all users. Also in the case of open source you can at least get support from any developer interested in the project and willing to help. In the case of proprietary software the dependence from the owners wills are higher.

So fundamentally the Ubuntu forums are populated by a quite homogeneous community of users that are aware of common elements like Linux, open source, software platform, common repositories... The MeeGo users will find themselves in a different situation. A core group will also care about Linux, open source, software platform, common repositories... but it is expected that a majority will actually care primarily about the device they got, with a customized UI and a bunch of apps, some of them unique to their vendor and some of them common for everybody.

We can see this as a fragmented community or we can see this as a very diverse community.