While I booked a shared transfer it ended up being just me in a private car. Vehicle was very new and in great shape. The driver was very polite and efficient. Total drive time from my Hotel Hilton Millennium to the airport was just around 1 hour in rush hour traffic which is normal.
Will definitely use this service again if I'm in Bangkok.
This was a problem. When I arrived, there was no one waiting for me. After wandering around for a while, I found the Thai Tourist Department counter and they referred me to the company I had booked the transfer with. I spoke with their on-ground representative who had no record of my booking. However, when she called the office, they located it and sent a car for me. It took a good 45 minutes to arrive. They came through in the end but it was a hassle I didn't need after 21 hours in transit.