It's too soon to call it, but Twitter's meteoric rise may be a thing of the past as the service has seen the same traffic numbers for the past few months. Facebook on the other hand is growing at a steady pace and is coming close to 100 million users in the US, according to the latest numbers from comScore. Facebook gained 3 million unique visitors in September in the US, which is not exactly spectacular but, considering it now has 95.5 million unique visitors, up from 92.2 in August, any sort of growth is impressive.

Twitter traffic on the other hand has remained flat for the past few months, with the microblogging service having managed to gain just 100,000 new visitors to the site in September, reaching 20.9 million unique visitors. Many users – as much as half – connect to the service from their mobile or desktop clients so the traffic numbers for the site itself may not show the whole picture. But, while the actual size of Twitter's audience may be a lot bigger, the growth rate may be a lot closer to the one portrayed by the comScore numbers and numerous other measurements.

It's also interesting to point out that, while Facebook is now almost five times larger than Twitter, it is the giant social networking site that is looking more nimble and is gaining users at an unrelenting pace while the microblogging site, which has been the social media darling for the better part of this year, has leveled off.

Twitter has some big ambitions as it wants not only to overtake Facebook, but to one day reach one billion users, roughly two thirds of the world’s Internet population. The gap between the two social networks though is widening in the US and is already much bigger worldwide, where Facebook has already reached 300 million users and, by all estimates, will easily reach 350 million by the year's end. Twitter on the other hand is billed at somewhere above 50 million. It will be interesting to see if Twitter traffic manages to pick up again, if the users are in fact connecting en masse with mobile and desktop clients or if this is indeed as good as it gets for the microblogging service.