I have been in the market for the S95 and have too noticed the price coming up. Although, it seems when the S100 becomes available, the S95 drops again. I think it is supply and demand on the S100 side - when there are no S100 available people decide to buy the S95 and thus the price jumps a bit.
Back to the original question, I chose the S95 because it is a backup camera and one the wife uses the most. I chose to take the $150 savings and put it towards another lens for my 5D II. Use your money wisely! =)
While that's smart thinking, $150 is about 7.5% of the price of a USED 5D2. Is that savings worth getting a significantly inferior camera for? For me, it wouldn't be. But, I've been waiting for the S100 since the S95 was announced (so about 2 years) and I don't plan on replacing it for years to come.