I rarely use taxis, but last week I was in a strange city* on a tight schedule, so I got a cab from outside the railway station (I could claim expenses, so didn't worry). Cost for about 2.5 miles across the centre of the city - £7.00.
Later, I found out that some other delegates were going back on the same train, so we asked the organisers to book us a taxi. Same journey in reverse in roughly the same traffic - £5.00 (though it was a private hire rather than a cab, and, the organisers, being a hospital, probably have a contract rate). This caused some discussion amongst the other three, who had got a taxi at the same time(-ish) as me (they had been on the same train). Their journey had taken ten minutes longer then mine (they didn't recognise any of the streets taken on the return trip) and cost £20! The point? Yes, there are some robbing bastards in taxis.
However, in Prague the taxi drivers are so powerful they have effectively blocked an extension of the tram system to the airport because it would eat into their ability to gouge tourists to the tune of up to 300%. We could have it worse!
*Glasgow - a very strange city!