I had to deal with Allstate when someone hit my wife's vehicle. It was a pain. It was their client's fault, and my wife's car was totaled. They didn't want to offer me jack squat. I went rounds with them, and never agreed to their low-ball offers. Ended up working out okay, but had to talk...
Like stated above, DO NOT agree to their first couple of offers. Personally, I'm not sure I would accept anything less than replacement value. I've been down that road before, and THEY WILL up their offer. They are just hoping that you feel like you have no choice, and will eventually relent...