According to the report, Gmail registered 29.6 million unique monthly visitors in December 2008, representing a 43 percent increase from last year's 20.8 million. Windows Live Hotmail's monthly unique visitors on the other hand were reduced to 43.5 million from 45.7 million in the same period. Google still has a long way to go to catch up to Yahoo, which also saw a decent growth rate of 11 percent year to year, but it's realistic to think that it could happen as soon as 2011 if you look at current growth rates.
Google was a late entrant to the web mail space compared to its rivals but has contributed a lot to the market since its debut, offering 1GB of storage at a time when 2-4MB was the norm and introducing simple yet innovative new features such as auto complete and a conversation style way of reading your inbox. On top of that you have the Labs feature offering you lots of experimental functionality and regular updates. Both Windows Live Hotmail and Yahoo! Mail have reason to feel threatened right now as Gmail is poised to become the number one webmail provider.