I voted "serious", but I consider myself to be partly "serious" and partly "hardcore".
I don't have or want a dedicated gaming room, but I certainly consider gaming one of my primary hobbies. I have a pretty sizeable collection of games and supplements, though it's more like "dozens" than "hundreds" or "thousands".
I don't think about my gaming in terms of GNS or GDS, but I frequently read RPG.Net (and, less often, here or the official D&D forums) so I'm quite familiar with the theories behind the labels. I know, for instance, that you don't properly call yourself a G, N, or S gamer, you describe your actual play as G-, N-, or S-focused.
I have played in multiple campaigns in the past, even the recent past, though I'm not really playing now, and only running one game infrequently.
I think about gaming and visit gaming forums every day I have internet access, but I go through patches of intense interest and patches of slackened interest. Right now, immediately after BlizzCon, I must admit I'm more jazzed about World of Warcraft: Cataclysm than anything for pen-and-paper gaming (though I did just order Geist: The Sin-Eaters, so that will probably excite me once it arrives).