You know...just for fun, I did a search for the word in its two main forms (the one that ends in "er", and also the slang form ending in "a") on iTunes. I stopped counting at 400 results, but there were certainly more (granted, some were duplicates, but even so...).
And while iTunes itself censored the word partially (e.g. "n***a"), I'm pretty sure the performing artists themselves probably sang the actual word. Not that I bothered to find out; hip-hop really isn't my thing. I'm pretty sure, though, that iTunes won't be releasing edited digital booklets with the albums these songs derive from, in which the offending word is similarly replaced with "slave".
And what about a more modern classic, like "Roots", which makes prolific use of the term? Will newer publications of that anti-slavery opus be similarly censored, if released in the future?
I get that it's a nasty word with a nasty meaning...but this idea of revising Huck Finn still just sits wrong with me. It's a story about a time in American history which wasn't all unicorns and roses, after all. The portrayal thereof is not ruined by the word change, of course, but it is in some way diminished.