In order to address a few questions I have received:
1) The terms and conditions provided on the website were provided to me by Hyatt Gold Passport. Hyatt customer service may not know about the promotions (yet), but the terms and conditions are correct.
2) The diamond trial begins 30th July. If you register after the 30th July, nights will be counted from the 30th July.
3) All gold and platinum HGP members will be enrolled in the diamond trial (as long as you agree to t+c on website), regardless of whether you have had a trial before.
4) At the start of the trial, those enrolled will receive 4 suite upgrade certificates. If you do not qualify for diamond these will disappear after the trial, although you can use all of them before the trial runs out. If you do qualify, you will receive a further 4 certificates in March 2013.
5) If there are 2 HGP members sharing a room, in order for both to qualify for the HGP promotions, you will need to book 2 2-night stays (1 in each name) and ask the Churchill to link the stays. You must have a qualifying stay hit during the do in order to qualify for the promotions.
6) With regards to the tiered bonus promotion, the bonus points are awarded in one go past 19 nights i.e. night 19 is worth 25,000 points and night 30 is worth 50,000 points - there is no bonus for nights inbetween 19 and 30.