I happened to get rear-ended at a fairly low-speed in a relative's car, but this is about finance, not me.
Called insurance, and they sent their rep over for an estimate. Car wasn't totalled, but they would pay up to $2700 (I think it was) to have it fixed at a shop of our choice.
If you ask them, they can pay you directly for self-repair. Going this route, they only pay for parts value (excl HST) and half the labour cost. Which in this case, worked out to $1700.
This does come at a bit of risk if the damage is more than expected, or if the repair you arrange isn't top-notch.
Nearby neighbourhood mechanic fixed it for $950.
There's also a very long thread here at RedFlagDeals on getting top-dollar if your car is a writeoff: http://forums.redflagdeals.com/non-faul ... ey-430232/
From what this sounds like, you should always reject the first offer if your vehicle is a writeoff, because there is an amount that you can force them to pay. But for repairable cars, insurance can offer as little, or as much, as they like when a vehicle is not a writeoff.