According to ComScore Media Metrix, as of June 2009, Yahoo! Mail is still king of e-mail with around 106.2 million users, registering a 22% increase in membership since June 2008. Windows Live Hotmail comes in at 2nd place with 47.1 Million users but with only a 2% increase in users since last year.
Google fans don't fret!
While Gmail ended up only in the 3rd spot, it registered the highest percentage of membership increase at a whopping 46% from June 2008 to June 2009 -- Definitely not bad for a 5 year old service (Gmail was released in 2004, Yahoo! Mail in 1997, Hotmail in 1996) IMHO, at this rate, it is not unlikely for Gmail to lead the pack 'eventually' -- I'm predicting in 3-4 years if fate would continue to be kind to Google.