All of the hype around the Olympics has put a mega-magnifying glass on the micro-blogging Web service Twitter. First it was the main outlet for people to give instant feedback about the opening ceremony, then it was the sounding board about the time-delay that NBC created for the Games, and finally it was one of the major reasons that Olympics officials and telecasters gave for disruptions in the athletic updates during the cycling event this weekend. 

Now, the word is that Twitter has passed a milestone, reaching more than 517 million accounts, according to the Paris-based analyst group Semiocast. 

It's hard to tell just how many of the accounts are very active, but of the more than half a billion accounts created on Twitter, 141.8 million of those users in the U.S. This secures Twitter as the second largest social site behind the 955 million accounts on Facebook.

Despite the American dominance in the number of accounts, according to Semiocast's findings, the top three cities in terms of the number of tweets created are Jakarta, Tokyo and London.

The firm says it based these figures on a sample selection of 1.058 billion public tweets in the month of June.

It also notes that while Tokyo is one of the most active tweeting countries, growth there is maturing and, therefore slowing down.

US cities that ranked in the top 20 were: New York City (ranked number 5), Los Angeles (ranked number 8), Chicago (ranked number 9), Miami (ranked number 18), Atlanta (ranked number 19) and Houston (ranked number 20). 

I personally was shocked that San Francisco didn't crack the top 20, but you will notice that the cities included in that top tier are also much larger metro areas than the seven-square-mile tech city. Twitter’s home market of San Francisco accounts for only 0.2% of all tweets.

Currently, Brazil is the fastest-growing Twitter country, with 41.2 million users, up from 33.3 million in January. 

Other adopting Twitter a major social communication device include Indonesia, with 29.4 million profiles.

Semiocast also states that Arabic tweets are growing in number on the site. Arabic is now the sixth most popular language on the site, accounting for 2.8% of all tweets. Saudi Arabia’s user numbers were up by 93% in six months to 2.9 million.

It's also worth noticing that, despite the fact that geolocation has been gaining traction on Facebook and FourSquare, the geo-location feature is only used 0.77% of the time on Twitter.