…When you go thru the truble of logging ont the forums thru the DSi browser.
(doing that now) ;)

... when you visit GOG in the toilet on your laptop while you're crapping. (Ah, wifi...)

...if you haven't done any major upgrades to your computer in more than a year 'cause GOGs don't need it.
...if you (are sad to) discover you fail to keep up with news about new hardware (for the same reason).
...if, while looking at prices for various entertainment methods (theatre tickets, DVDs, movie tickets...), you keep thinking how many GOGs you could buy with that money.
...if you show little interest in the majority of new games.
(True stories...)
EDIT
+1: ...if you should really, really study for an exam that comes next day, and yet you play GOGs (in my case, Sacred)/post in this thread instead.

...you are not interested in racing games, yet bought TOCA 3 simply because GOG is taking it off the shelves

present.

present

+1

... you are now sitting & practising FlatOut jumps although you've never heard of this game before.

I know I did, especially when I did research on the game. Have not tried it yet.
........you start researching old games that appeared on GOG.

eww! So not touching that laptop. =)
......When you give out to much information about things we don't need to know when you use GOG.

...you vote for highly demanded stuff on the Wishlist you don't even want so your fellow GOGers may one day have it.

...if you gift and receive GOGs for special occasions.

You're a bit annoyed that you can't use gog.com though pocket IE on a PDA

Opera 9.5beta works fine though... yes, I´m typing this on my phone just to make sure I´m not lying.

... you've laughed harder at some of the posts on these forums than you have at the routines of some professional comedians
...Tuesdays and Thursdays, the first thing you do when you get to work is check GOG for announcements

you know you're a gogger when....
you've thought I really want to set up a direct debit / standing order with GOG.com