I got my invitation a couple of weeks ago and booked my test drive for next weekend (12/13 Aug).
Don't know how you qualify for the invitation as I already have a 350 but i am intending to change it for a MY06 next year. Other ppl I know who have had a 350 from new have not received an invite!!!
There is a 300 mile max limit on the test drive and you need to pay £500 on your credit card which is returned when the vehicle is returned in 'satisfactory' condition. Might be worth establishing what they mean by 'satisfactory'!
I have given the tel no to someone to get a drive, but they refused without the invite - however he was directed to the Nissan website and managed to get a test arranged from there.
Dave.