Well, I think most people here are just doing this for fun, but mascots can serve a valid purpose:

They make something more memorable for people who have visual memories. The name "maemo" is not going to stick in everyone's minds, but if you put a memorable cartoon figure next to it that may help them remember maemo. That's why so many companies use product logos, so that people remember the product itself.

A lot of memorisation techniques rely on people imagining creatures or objects that represent abstract ideas, because they may find it easier to remember an image of a solid object rather than non-physical facts and figures.

And if you look at open source, most of the logos are indeed pretty silly cartoon animals but they don't seem to have harmed the movement's chances of being taken seriously. A lot of Linux-based consumer devices now have a friendly penguin on the box.