The Web is a funny creature. One day, you’re king of the world; the next you’re wondering where everyone went. Web users are fickle, willing to jump into the arms of another service in a heartbeat, and always looking for next shiny object.

Maybe it’s my eternal reservations about Facebook but I have a hunch there’s a chink Goliath’s armour. It may be small but Facebook’s dominance shouldn’t be taken for granted. The whispers start when hard-core social media users stars talking about how they rarely use Facebook because it’s “full of crap”. This comment was made by a PR executive who makes a living selling social media strategic and tactical services to clients.

Now you could dismiss this comment as simply a member of digital “elite” getting tired with his favourite toy. But another way to decipher this statement is it is an indication of a quiet movement starting to bubble up. One of the realities facing Facebook is the more mainstream it becomes, the less cool it becomes (assuming Facebook was ever cool!) As more companies and adults storm onto Facebook, its appeal among younger people diminishes.

At the same time, Facebook’s hunger to add more services (Places, e-mail, etc.) threatens to put it in “portal” territory -a place in which you can do everything without going anywhere else. (Anyone remember AOL?) It’s a compelling and potentially lucrative strategy but, at the same time, it is making Facebook a busier landscape with lots of bell, whistles and noise.

It is this cacophony that may start to drive people away from Facebook because every new service takes it farther away from its roots as a place for family and friends to share updates and photos. Maybe this explains why the person above lost his interest in Facebook.

Of course, millions of people continue to storm onto Facebook every week, and there are some people who believe Facebook will have one billion users by year-end. The thing about Facebook is it’s like a red-hot party – no matter crowded and uncomfortable, people keep on coming because it’s the place to be. But at some point, people may start to think there has to be another place with good music but room to move and hear yourself talk.

Facebook is far from reaching this juncture but it would be ill-advised to dismiss the concerns of people who are unhappy with the service. The only problem right now is there’s no other party happening with enough people to make it interesting. Until a legitimate rival to Facebook emerges, people leaving will be a dribble as opposed to a stampede.

More: If you’re looking for signs of Facebook’s growth, you can look no farther than its hunger for more office space.