Absolutely! I love drawing in sketchbooks and I'll usually try to top my competition if I am able to. I used to carry sketchbooks around all the time when I was a kid at conventions, so I know how fun it is to collect peoples' art. A couple things about this....

1) At no point will I *ever* charge for this. I always used to hate these artists that could look at a 13 year old kid in the eye and actually try to get 25 bucks out of his pockets for a 3 minute sketch. Commissions (i.e. full drawings) are one thing, but a quick sketch? Come on. 

2) I'm not the fastest artist in the world...I may ask you to leave your sketchbook with me and come back in an hour.