Nobody has any doubts that Facebook is huge at this point. The social network reports 350 million monthly active users, analytics firms show huge traffic coming its way each month and Facebook Connect is everywhere you look. But the numbers can be a bit misleading, registered users aren't the same as the number of people actually using the service and a user who visits twice a month is not equal to someone who visits several times a day. This is why a new stat coming from Facebook itself may prove to be the most relevant yet, 175 million people log into Facebook every day.

Whichever way you look at it, it's huge. That's half of the people regularly using Facebook, i.e. logging in at least once a month, visiting the site each day. To put it in further perspective, it's more people than Facebook had altogether last year. The social network started in 2009 with 150 million active users and more than doubled in the last year worldwide.

Interestingly, half of them used the social network back then too, according to CEO Mark Zuckerberg. Many believed that it would be hard for the social network to maintain this level of engagement as it grew, including the people at Facebook, yet it doesn't seem to be dying down.

In the US, the country where it already had a significant presence, it did an equally impressive performance, starting the year with a little over 50 million monthly visitors and ending it with more than 100 million. No one is sure if and when this is going to stop, it will have to stop eventually, there are only so many people online. But with one and a half billion people online in total, there actually isn't that much more room to grow. At its current growth rate or even a decreased one, 500 million by the summer of 2010 doesn't seem so far-fetched as it did a year ago.