Tried Uber a couple of times in HCMC so I thought I'd give a quick report.

I tried once at the airport. Driver didn't show up. I tried once more for a trip within HCMC, which was fine.

• Took about 8 or 9 minutes to arrive.
• Even though advertised as Black Car, the car was the same as a normal taxi (Mai Linh or Vinasun).
• Drivers are about the same (English skills are not great).
• No water or other amenities in the car.
• Price was about 20 or 30% cheaper than a normal taxi.

Taxis are easy to find so I doubt I'll use Uber much. If they had nicer cars, I'd probably use it though since I find normal taxis pretty cramped.

I do think it might be useful for some people, particularly if...

• You're looking to save a little money.
• You're off the beaten path, need to call a taxi, and can't speak Vietnamese.
• You're concerned about accurately communicating your destination to the driver. (Uber let's you input the destination into the app).

IMHO, in cities like HCMC and Tokyo where they have very good taxi service, I think there is less need for a service like Uber although I do think there might be a niche for a reliable, premium (black car) service, which is priced at a discount to existing options.