According to a study released by Nielsen/NetRatings [PDF], Meebo is the instant messaging solution with the highest US growth in the last 10 months. Meebo, a web messenger that lets you connect to Yahoo Messenger, Windows Live Messenger, AIM, ICQ and Jabber/Google Talk, increased its US user base from 434,000 to almost 2 million. In the same period of time, Google Talk grew from 904,000 to 2,25 million users. It's unclear whether the study only included Google Talk's desktop client or it also considered the web interfaces from Gmail and iGoogle. The more powerful Skype has 2,6 million users in the US.
Meebo became popular because many schools and companies blocked access to instant messaging clients and their web versions were almost unusable. Of course, Meebo was also blocked, so it came up with an HTTPS version. Now even if Yahoo, Microsoft, Google and others build online interfaces, people still prefer Meebo, the all-in-one messenger.