Sneak Peek is not a big deal. Yeah its a press event but its just a short overview of gear. Typically camera companies do not show their just announced DSLR there, Compacts yes, but they hold off till tues (first day of show) to unveil the big guns.
I will be attending Sneak Peek, and the ultra exclusive press event Digital Focus (editorial staff only) thats that evening in which Pentax will also be at and is said to be showing something new. Past that I have no clue.
Canon is not there because its a big CF (every blogger and their mom can show up really) and they dont need the extra attention, Nikon usualy isn't there either. (They both attend Digital Focus, not really associated with PMA, but "happens" to be at the same time, its a Private PR event really)
Sony is having a special press conff too so thats prob why they are not there.
Dont worry you can keep up to date via the site I work for (linked threw my blog) I will not post it here as I do not feel to give a free direct plug but will link if I find something big for Pentax