Well the speculation is quite interesting and that website. I do however believe that to think that Dumbledore is still alive is wishful thinking from those who don't want to let go.
At the end of HBP it shows us that Harry's made a firm resolve to go after the horcruxes himself. I believe that the 7th and final book will be mostly about Harry, unlike some of ther others. I think the book will aim at Harry growing emotionally and magically so that he can find the other horcruxes and destroy them. He needs to do this alone, at this stage recieving help from a thought-to-be-deceased Dumbledore would be almost like cheating and once again Harry would be the hero of the day only because he recieved a phenominal amount of help from others.
Also I think it would be extremely cruel of Rowling to bring back Dumbledore in the next book, it would be like her saying: 'haha, he's not really dead, fooled you! You all cried for nothing!' There is, as we see in this website, evidence that Dumbledore perhaps is not dead. It did say though that when Snape "killed" Dumbledore that his face had 'hatred' and argue it all you want but I don't think that was self-loathing. I think that the inconsistencies mentioned, for example Dumbledore being thrown from the rooftop were just that, inconsistencies. We're dealing with a writer who by no means is a Tolkien or Lewis. Whatever points she looses in writing style is made up for in plot. I believe that it would have been impossible for Rowling to not have inconsistencies in her plot. She wasnted to dramatize Dumbledore's death by throwing him off a rooftop, she gave no thought to the fact that the other two or three Avada Kedavra curses in the book had the victims only falling over. Or perhaps Snape's hate for Dumbledore was so strong that it jettisoned him off the castle.
My last question: why did Snape perform the Crucio curse on Harry right before he ran off the castle grounds if he was on Dumbledore's side? Might it have been because he wanted to make sure Harry really believed that Snape was death eater and to expell any thought he might have of Harry thinking that Snape killed on Dumbledore's orders?
We'll see what happens when the seventh book comes out.