There is a fantastic talk by Kevlin Henney where he deconstructs the SOLID principles as each being either misunderstood when they were written - or frequently misunderstood after. It was done here:

http://scottishdevelopers.com/tag/solid/

http://sydney.yowconference.com.au/

I won't spoil it by writing all the points here - just some pearls.

* The Open/Closed principle is redundant because it is already covered by the Liskov substitution principle.

* Bob Martin's view of the Dependency Inversion principle is in fact the Single Responsibility principle.

He suggests 5 more principles - but I won't spoil it by listing them here. Go see it!