I saw this by w7west over on Darkwynn's blog:
"Spam might work with marines but what a boring army. You will need to think in more than one dimension with your dark eldar. You can't spam since every unit excels in a specific area."
This makes a lot of sense to me. Dark eldar are a lot like their cousins, the eldar. I'd never really thought of this before until I read it there. In reality it's not completely true, for instance some players love to spam mechdar lists with Dire Avengers in wave serpents with three Fire Prisms. I've even had people tell me they take three Prisms because that is the maximum allowed... Hee! Anyways going back to the quote I think it has a lot of merit and I'm going to start approach building lists for dark eldar using that as a central tenet. I have noticed that you are going to need some specific units such as an Archon and probably Haemonculi to create competitive armies.