I can confirm that the "thank you" email has now been sent to attendees of the first day UK developer launch. If you only attended the second day, that email goes out at midnight tonight. Why? Different systems apparently.
So why is this important anyway? Because you use it to make your choice of software (either Windows Vista or Office 2007). So please look out for it and make sure you make your choice asap, there is a 7 day deadline for responding. After that it will be too late!