Hm...strange. AGDQ started today and Spinosaurus hasn't mentioned it.
Whelp, I might as well explain what I can (though not as well as him, he gets pretty into it).
AGDQ is the first of two Speed Running events during the year that runs from today, the fourth, to the eleventh.
This particular event's donations go to the Prevent Cancer Foundation. To go with the event, Humble Bundle is running an
AGDQ 2015 Humble Bundle, with however much you choose to go to the charity as well. Along with that, the Yetee sells a number of (pretty incredible) shirts during this time a year (They do so year-round, but only during GDQ do we see an influx like this).
It's quite a bit of fun, coming from someone who was completely disinterested in watching speedruns prior to last year's AGDQ. Apart from knowing that you're contributing (which you probably will, in some way), the event itself can be exciting and you generally come out of it with more than you came in with (metaphorically...probably). Maybe you'll watch speedruns for games you own and then want to try out some techniques yourself, or maybe you just want to see a guy beat Super Mario 64 as fast as he can one-handed. It's not the biggest event, but it can feel like it at times, especially when someone pulls off a rather dicey technique and a roar of cheers follows.
I recommend that you guys check it out, whether you like Speedruns or not; after all, it's for a good cause.