I bought the clutch in black and was talked through the monogram service by one of the very helpful and lovely sales assistants...
This is the result.
There is a good range of letter colouring options, and you can choose to have small or large font (I went for large in the Lilac, as it looks more white on the dark clutch). Altogether the service comes to around £95 pounds, although I got a student discount on the bag, and paid £85. It's admittedly a lot of money for a clutch bag, but it's definitely an investment piece that I'll keep forever, and it's just so special! The whole process takes 2-3 weeks (but it's usually closer to 2) and then it's ready to collect at Dover Street. I literally want everything I own to be monogrammed now...