I did the Palace ride the first year they did it (2006) - OK route with a few bits on the towpath.
Organisation was OK-ish ... although they under-estimated the speed at which riders would cover the course and the drink stops etc weren't set up ... I did it on a fixed and apart from one short lung-buster near Virginia Water it was easy. Started at 0800 - Windsor at a bit after 1015 IIRC. Great to ride down the "Long Walk" (usually not allowed) to Windsor Castle.
All the stuff they put on at the end is a bit of a waste of time - I finished and rode to Slough to get the train home.
If you're in the Midlands (or anywhere really) try the MacRide on 7 September at Stratford-upon-Avon - the charity ride with a difference - over 95% of the money raised goes to Macmillan Cancer Support (last year : £25,000+ with <£200 in costs) - secure online booking at
www.macride.org.uk Rob