I used to be merrysphynx, which means very little because I rarely commented here.

Anyway. There's nothing wrong with writing the interesting back story if that's what you've got straight. It can really help with writer's block, because at least you're writing something, and even if you think it's utter crap, it'll give you something to work on later when you feel less creative and more revise-y. Plus, it can help generate ideas for the present day, because you might write a sentence that sounds like foreshadowing, or whatever.

At least, that's how it works for me. Your brain might not work the same way, but mmph. Worth mentioning.