Taxi drivers - already replaced by people driving their own cars, or shared cars in the city centers.
Limo drivers - the driver is ALL the service, which is why they wear livery. If it was just keeping drunk prom-goers from driving, they would call a cab.
Couriers - Damned if I know. I suspect that unbonded couriers get replaced by FedEx/UPS already, and bonded couriers are there to maintain chain of custody.
Mitt Romney's chauffeur is not a driver, he is security, well-trained in anti-kidnapping offensive driving, the non-criminal version of Joe Valachi when he was the driver for the first Capo di Tutti Capi (see the movie The Valachi Files). He will be the last type of driver replaced, along with bank robber wheelman.
NASCAR drivers - might become the off-time job of moonshiners, again, like it started out. Those people started out paying to race go-karts when they were kids, after all. Formula One definitely dies when the first computer wins the World Championship, and polo players start accepting sponsors and visible ads.
BTW, the reason that the London Underground trains still have engineers is that the maintanance workers went on strike, or at least threatened to, unless their "brothers' jobs" were preserved, sometime in the past. It is called featherbedding and also explains why non-passenger trains have conductors.