hmm oh yeahand given the subject of the original post,

i would say stay demo while you level, or try affliction for a while, destro is no good for levelling as you will have to spend alot of time drinking. then go demo or affliction for early raiding depending on your preference, i would suggest trying both. if you get to the leetest gear stage you will most likely go destro.

trying out different specs for different things will help give you a better understanding of warlocks and their strengths, and you will find a spec that will suit your playing style/ find fun