Anonymity and impunity are the bane of empathy. This is not a new thought (see: http://en.wikipedia.org/wiki/Ring_of_Gyges ), but in an electronic world where we cannot even see the damage our words may wreak, the restraints are loosened even more.

As far as solutions are concerned, having identified the problem I would posit that you're most of the way to the solution already. Just keep it in mind and exercise self control.