As so many others have touched upon already, the problem with CN is in its definition. (Un)fortunately CN isn't the only alignment suffering from a bad rap. LG is another alignment that seems to carry a burden with it.
Myself, I stick to the definition for alignments provided by the Dark Sun expanded boxed set. At least they tend to make sense to me.
In short, the definitions of the alignment fall into the following categories:
Law = rational thinking
Chaos = emotional thinking
Good = for the party/greater good at the expense of yourself whenever possible
Evil = selfishness/Me me me and no one else.
It basically means that a LN character will do whatever seems most rational, regardless of whether it serves him or the greater good, a CN character will use its emotions to make decisions, as in "what feels right, right now". A NG character will do whatever is best for the group/greater good regardless of whether the action is rational or emotional, and a NE character will do whatever serves him the best regardless of rationality or emotions involved.
To illustrate with an example, I can imagine seeing a NG, CG, N, CN, NE and CE character sitting outside the courthouse waiting for the BBEG to be convicted, only to off him as he leaves. A lawful character IMO wouldn't consider it, as it isn't rational.
Similarly I can see a LG, NG, LN, N, LE and NE character choose to not oppose authority in a city as it makes rational sense.
I'd see LG, NG, CG, LN, and N all go down the road of self sacrifice if it's either the rational or to the benefit of the group to do so.
I'd also imagine a N, CN, NE and CE character steal/pilfer items on a whim, if it serves them now.