Activity does not mean anything, anyway. It is a complex and seriously flawed (thus rather useless) measure composed of several parameters which are not evaluated in a fair manner at all. It's a Sourceforge feature, and BerliOS uses a modified version of Sourceforge.
We had a 40% activity rating for several months, although we clearly were more active on a daily base than some projects which were listed with 99.99%. That was annoying because those projects would get top-ranked on the front page while ours would not.
As you can see, we have changed a few strategically important points in the mean time, so our ranking is better now.