A taxi from central London to Heathrow can easily cost 90 quid unless it's a booked minicab which then drops it to 40-60 quid, you can take the heathrow express but thats also 40 quid both ways + additional fare to get to paddington.
I would love to use this service both for the speed and the experience (unlike the scenic traffic jam you get otherwise) just to get a sky high tour of NYC...
Too bad it's never gonna scale, there probably will be huge limits on the amount of luggage you can take (which will make it either very expensive or completely unusable for international travelers) and the costs are going to go trough the roof quick enough.