Let's speculate! For background, I am a neurobiology student. Ergo, I've got the requisite chem n' o-chem under my belt. (Would like to fit in some biochem, but I don't know if that's possible right now.) From my own perousing of the material on the internet, it seems that carbon is really the only molecule we can do much of anything with, considering it's the easiest molecule to bond to 4 atoms stably and it's so freaking common. Silicon and phosphorus-nitrogen have been suggested, but neither system is stable enough to evolve life (because life always takes the easy way out; what that is is frequently beyond the comprehension of us idiot humans). So - the anti-carbon-'chauvinism' movement is bunk. However, there's the question of chirality, and can carbon-based life require different sets of nutrients? Arsenic compounds, etc? What characteristics can be regarded to be 'universal' as regards carbon-based life - i.e. there is no way we can presently think of that they can be contravened at all, barring something totally out of the blue?