This is a question that I thought would be interesting to discuss that was motivated by the off topic discussion in this thread.

If your applying class/id attributes on the basis of whether or not you need to style a specific element aren't you condoning the mixture of structure and presentation? Thinking of the mark-up as a separate entity shouldn't it be written putting aside any need for presentation?

Doesn't the idea of applying attributes without considering how they may be presented support the notion of loose coupling between presentation and structure?