Regenerative braking is often a misunderstood part of electric cars. Almost everybody knows that electric cars can have regenerative braking, but most are unaware of just what is happening in the process of slowing the vehicle down. In fact, I would guess that there is a large number of drivers who don't even know what is happening when normal disk or drum brakes are slowing down their car. I think that many would find it interesting to know that much of the work going on at Tesla to make regenerative braking work properly is being done in software. The motor controller of any electric car is in charge of making the regen power recharge the batteries, just as it is in charge of making the battery charge provide forward motion. So, just as the power profile of the vehicle can be "tuned", the reverse is also true, and the braking force can be "tuned" as well. As Greg writes, there are differing opinions on how the regenerative braking should feel. Good reading, if you ask me.
Perhaps it is also worth noting that other manufacturers have worked through these same compromises already. For instance, check out Sebastian's post on riding in the Phoenix Motorcars SUT. Vectrix has done something completely new with their electric scooter, where regenerative braking occurs when the throttle is moved backwards, leaving the normal brake lever alone. There's more than one way to... you know the rest.
[Source: Tesla Motors blog]