Just used Uber for the first time, Roppongi Hills to Haneda. Here are my thoughts:

1.) The car arrived within 10 minutes, just a hair earlier than quoted. Since I was completing my check out, I texted the driver via the app and asked him to wait at the lobby. He was there and in sync with the hotel bell desk staff, awaiting my arrival, bags had been pre loaded.

2.) Very professional, courteous driver, identical to every other cab driver I've had from MK Taxi, etc when pre arranging transportation.

3.) The vehicle was marketed as a Corolla in the Uber app. It was larger than a standard taxi, but not one of the "high end" vehicles I generally reserve via MK (BMW, Lexus) for trips to and from Narita. It was comfortable - nothing special. No ottoman like 5khours mentioned in his vehicle. I particularly like that in the higher end sedans that MK uses. That and the seat coolers which are very helpful in the summer. Regarding aventine's comments above, I concur. Coming from sleek brand new Cadillac Escalades in San Francisco, these "standard" type sedans are a bit of a let down.

4.) Cost was almost exactly $75 USD, near identical to what I paid last time with a standard taxi to and from the same locations. Convenient to pay via the app, although AMEX immediately texted me a fraud warning. I find that hard to believe as I use Uber (in the States) all the time, and I haven't had an AMEX fraud warning in YEARS, even when using the card in SE Asia and other areas more prone to fraudulent charges.

Overall, it was a decent experience, but I see no real need to do it again. For my regular NRT transfers, I'll stick to my tried and true MK Taxi (although I am a bit curious to see how Uber would compare fare wise). For HND and other intra Tokyo routes, I think I'll simply continue to hop in the first available cab.