Janus brought up the point that for silicon reactions to take place easily enough the conditions would have to be extremely warm. But isn't it that as pressure increases, temperature increases (trying to remember back to High School science)? If this is so, what about a planet (we will assume a "rocky" planet and not gas) large enough and at the correct position to its star that it could have a normal gravity of 2,5,10, etc. (whatever would be neccessary) Gs. Underneath what ever atmosphere existed, and maybe then under water or another similar liquid, the combined effects of gravity and atmospheric, as well as water, pressure created the high enough temperatures?
Also, the point has been mentioned that chains based off of carbon are capable of being much longer than those of silicon. But chains still can be made, right? Would that then, should the possibility of life arising around silicon being true, limit this life? Something not as diverse as what has happened at Earth? Allowing only a few prominent "species" to exist? And then even at that, they remain simple. Single celled, or simple multicellular life forms; could they arise from these conditions? It need not be more intelligent than, lets say, bacteria.