10k new users posting xkcd and penny arcade comics would be. I can go to the xkcd/PA site to view the comics when I feel like it. I can go to fark/reddit/digg for humor. There is no need to make this site equal in content to them. I'm not saying they are bad, but I don't see the point in duplication.
10k new users might be a problem, in the same way that the flood of new Internet users from AOL was referred to as the "September that never ended". Any time users flow in to a community too quickly, it is difficult to bring them all in to compliance with the social norms of the community, resulting in a change in those social norms which the existing community members usually do not like. It's one of the reasons people get upset about immigration.
