I almost missed my flight this morning (19th Oct, 2012) after making a booking with Travel Time. I had booked a cab previous night for a 5am flight. In the morning they refused to send a cab as they saw no booking. They also kept me on hold for 15 minutes and made me speak to 3-4 agents before declaring they had no booking.
My requests fell on deaf ears to arrange something. So please book at your risk - they are pathetic and unreliable. Agents I spoke to were Harry and Mandar.