Traffic numbers for popular sites saw some predicted trends in May but also some surprising developments. The most interesting part is that Twitter's rapid rise in user numbers slowed to a crawl last month according to data from Compete. The micro-blogging site grew a mere 1.47 percent in May, hitting almost 20 million unique visitors. Facebook on the other hand still had a healthy growth as did YouTube.

The news from Twitter comes after months of massive growth, with the service rising from a little over 7 million at the beginning of March 2009 to almost 20 million today. Monthly visits continue to rise, however, having increased by almost 7 percent in May to 134,536,240. The slowdown may be temporary or it may be a sign of things to come. As Twitter has invaded the mainstream news outlets for the last couple of months even its creators were worried that the exposure would eventually turn against them. Whether this is the case remains to be seen but it is troubling for the micro-blogging site.

Facebook however continues to boast very good results especially considering its size. The social networking site grew 8.54 percent in monthly unique visitors, from 104 million in April to 113 million last month. The number of visits also grew from 1.63 billion to 1.74 billion, making it the number three site on the Internet behind Google, with 145 million uniques, and Yahoo, with 135 million. MySpace on the other hand saw some modest increase with 0.46 percent in visits and 2.39 percent in uniques.

YouTube saw a small decline in unique visitors in May, falling to 76,5 million from 77,8 million the previous month. However, the online video site is seeing an increase in the number of videos watched, having grown 15 percent month over month in April to 6.8 billion videos according to numbers from ComScore.