>It's not very clear to me. Isn't setting the category to All the same as bypassing the category filter ?

As already answered in some other replies, the category filter is about the ability to not see specific categories. In the way the site is now, this applies pretty much everywhere, if not everywhere. There might still be some places where I would have to add this filter. Basically, we have three types of filters. The category filter, the thread filter and the twit filter.