does anyone have any pics of this happening?  i'm assuming it would be much more dangerous than a normal kaboom, because the chamber would be practically right next to your cheek?

I have not heard of one. Given the fact there are many bullpups on the market.

Steyr AUG
IMI Tavor
FN FS2000
L85
FAMAS
Valmet
M14.308 Bullpup
Bushmaster XM17
Ramline Mini 14 stocks
Mossberg 500/590
Hi Standard M10
And a few more....

With this many bullpups in the world I am sure that there would have been a picture of a kaboom on AR15 given the fact there are so many people who do not understand or hate bullpups.
I think they are great.

Ive never heard of one and Ive been shooting an AUG for almost 16 years. Ive been in the military much longer than that, much of the time working with coalition forces. Ive yet to hear of this happening with an AUG or other bullpup. In general its not that common with any military rifle. The only problems Ive heard of in general in the civilian community are with those who reload for ARs and M1As. I personally would not reload for a semi auto but to each their own.

I don't think it would necessarily be more dangerous.  While it is indeed closer, and could probably mess up the side of the shooter's face, the action at least would not be directly in front of the eyes, where a comparatively minor kaboom in a conventional rifle could theoretically cause blindness.  Also, much of the damage in a kaboom is the result of shrapnel.  With sufficiently heavy-duty materials, and/or polymers that bend instead of shatter, fragmentation of the receiver could be reduced or eliminated entirely.   Until some pictures of a bullpup kaboom surface, there's really no way to be sure what would happen, but I have trouble believing that every single manufacturer of a bullpup firearm neglected to consider the possibility of a kaboon.

Not every single one...the SAR21 series of bullpups do have a shield built in. But ,it was done to remove that fear right off the bat (whether real or imagined) so as to not be a sticking point when selling them to another country ect. I too have never seen or heard of any of the military bullpup rifles having a kaboom.

Only rifle I'd be concerned with is the Bushmaster M17, because it's possible for a round to slip past the factory barrel extension and get caught inside the handguard.  If you had been rapid firing with a red hot barrel and this happened, it could kaboom.