Have been doing "mail-chat" with vkvss since yesterday about various rumours and speculations regarding HBP.... and mostly it was about this book cover. Its the cover of the US Deluxe Edition and gives the most fodder for speculating out of all the covers released yet.
My theory (which is very likely wrong) is that Harry and Dumbledore are in someone's pensieve, probably Harry's own pensieve. The stocky guy is probably Frank (the gardener in the first chapter of Goblet of Fire) going towards The Riddle House in a replay of the first chapter of GoF. Harry and Dumbledore probably want to find something out so they are revisiting that memory.
What shoots this theory down is the knife in the tree trunk and the snake on the door of the house/hut. My theory can't explain them even though both seem pretty important. Also, as far as I remember, the Riddle house had at least two levels, this one doesn't seem to have (even though there are curious "eye-like" windows on top). However, the worst thing is that Harry seems to be clearly holding the branches around him which is not possible if he is inside a pensieve.. he should've looked more like an image and not really solid... :( Anyway, its fun to speculate.. :)
One thing is pretty clear though - Harry and Dumbledore are going to spend a lot of time together in this one doing very important stuff. Dumbledore will most likely take Harry under his wings teaching him advanced magic training him for The War. This lends some strength to the rumour that Dumbledore is going to die in this one, probably after making Harry ready for the days ahead. (this is JUST a rumour.. no strong evidence behind it.. so if he DOES end up dying, don't kill me for spoiling it for you... I have no idea who is going to die.. :) )
Meanwhile, JKR has answered the FAQ about communication between Order members on her site. Look at it here.