I'm about halfway through and I'm pretty sure I know what happens based on
hu-man's comment -- the last journal entry tells of some seriously creepy shit and then the next link where they're finally supposed to have gotten in leads to no where, meaning they were never to be seen again
The story's real entertaining, and very well written -- almost too well-written to be a real personal journal. Most journals (look at web blogs for example) aren't as well developed and continuous -- they're more like diaries.
You must also consider that he was writing for a specific audience since, for example, he devotes a page to explaining the details of caving. It's probably just a piece of well-written, compelling fiction, just as I suppose
John Titor is. Just like that, for those who "want to believe" it's even more compelling!
Oh yeah, the design's real annoying because of the color scheme. Which leads you to pay more attention, and perhaps tend to get more freaked out!! I wonder if that was intentional....
EDIT: I forgot to mention that the fact that he nicknamed it "The Tomb" seems overly constructed to create suspense...