HappyBB: MeeGo is Nokia's answer to Google's Android. The difference is that MeeGo is fully open and it is a full-blown Linux system which Android is not. One very important part of a software environment is also the tools for developing applications on it.
Nokia has over the past few years developed the developing environment called Qt which has gained wide spread popularity not just for mobile phone applications but also for
desktop applications. You see, everything you develop in Qt can be run in Windows/Linux/MacOS/*NIX/Symbian/Maemo/MeeGo. Examples of Qt based applications are VLC, Skype, Google Earth, VirtualBox. More info can be found
here (qt.nokia.com). This cross-platform compatibility makes it a lot easier for an operating system such as MeeGo to transition into Tablets or whatever than it is for say Android as its developing environment does not have that strong cross-plattform support and it is not as well developed.
Since MeeGo is a fully-blown Linux build; with it comes the full Linux userland. This means that anything that you can run on Linux can be run on MeeGo. Sure you may not want to run everything on MeeGo and applications such as OpenOffice, FireFox, Gimp, InkScape or Blender may not be useful on a phone since they are built for a desktop computer. But many applications are skinnable so in most cases applying a skin or user interface adapted for phones will solve the problems with applications such as Mozilla Thunderbird or Firefox which is a lot easier than rewriting the whole codebase which is often the case when porting applications to mobile phones.
Also any application you can run on Android can be run in MeeGo. The following is a video of a guy who runs Android apps on a Nokia N900:
Myriad Alien dalvik (youtube.com)
So there is no doubt that MeeGo can be a very strong competitor in the mobile market when it comes out.