Currently, once you go over a hundred, you'll probably turn the shelf off, switch to the list sorted by purchase date, and never look into your library unless there's an update or a new game to download.
Frankly I never use the list view despite having "too many" GOG games already. I recognize the games by cover so I need them big pictures. :P
And I don't think we really need separate shelves (in the sense of manually grouped games), I think what would suffice would be displaying games by genre, publisher, age or tags or something. Which doesn't mean that I don't like the idea of manually grouping games on different shelves. Frankly, I'd probably spend far too much time reorganizing my games then because I'm a sucker for this kind of stuff. >.<