The labelling of Nickelodeon as a kids channel is debateable because some of their best jokes and shows (before they went downhill) had enough depth to appeal to adults. Most notably, shows like Ren & Stimpy, Rocko's Modern Life and the late Invader Zim were filled to the brim with quirky innuendo, jokes and/or references that will likely fly straight over a younger child's head.
Since 2000, quality has been declining, and as of 2008 they have officially hit rock bottom, essentially airing five or six substandard shows back-to-back, occasionally (though this may not still be the case) showing some old programming during school hours so that older fans (now probably having left school) can still find mild enjoyment in the channel.
It is hoped by many that Viacom is simply going through a rough time and will pick up quality eventually, but as quality continues to decline, most older fans are giving up hope (which only makes sense given that it is a childrens channel).
Me: My young friend, you shall never know.