It all really depends on your reasons for leaving.
If you are leaving because you are unhappy with the conditions then I think you owe it to your self/colleagues/successor to clearly explain your reasons for leaving. This is more likely to be effective if you can do it without getting personal or unpleasant (it is also quite likely to have no effect at all, unless you are one of many with the same complaints).

Alt: I'd like to be able to make a comfortable living out of music, but who knows, I might find a reason to moan about that and still waste my time on here.

AltAlt: Is there such a thing as a dream job?
( tangledupinblue hairy badge with moving eyes, Tue 11 Oct 2011, 15:46, 2 replies, latest was 14 years ago)

AltAlt answer
Suzanna Reid's sex slave?
( sporters I’m sincerely gratitude to you, Tue 11 Oct 2011, 15:55, Reply)

As a slave you would not receive much in the way of remuneration
You might argue that your job satisfaction would outweigh this, but it will not pay your mortgage. And Mrs Cow would not be impressed when you come home complaining about a hard day at work.
( tangledupinblue hairy badge with moving eyes, Tue 11 Oct 2011, 16:02, Reply)

Not much difference to here then

( sporters I’m sincerely gratitude to you, Tue 11 Oct 2011, 16:06, Reply)

AltAlt answer
Mythbusters.
( Agnostic Antichrist Baltimora, Tue 11 Oct 2011, 16:00, Reply)

I think you said that before
and I didn't understand it then either
( tangledupinblue hairy badge with moving eyes, Tue 11 Oct 2011, 16:03, Reply)

http://en.wikipedia.org/wiki/MythBusters
TL;DR - Blow shit up, get paid for it.
( Agnostic Antichrist Baltimora, Tue 11 Oct 2011, 16:04, Reply)

Cracking choice sir!
Should Ms Reid turn down my application I'll start growing a walrus tache straight away!
( sporters I’m sincerely gratitude to you, Tue 11 Oct 2011, 16:16, Reply)