Info is now up on the Bletchley Park Trust website as well. In my opinion, the hardest decision people should be making is not whether to join the trek but which charity to raise money for - Bletchley Park or The National Museum of Computing. Due to the financial logistics, you can only choose one. :-(
Also if you ARE signing up, don't forget that ours is the trek that departs on April 24th, 2013. And you don't have to be UK based to join us. We can figure it out if you are coming from another country so feel free to enquire.