There are up to twelve purple states or swing states as of 2012.
Almost all of the so-called purple states lean Dem and they are getting bluer like VA. The Dems have won the popular vote in 5 out of the last 6 elections. Obama won his elections with the two highest vote totals in US history--by far.
Immigration is fueling the changing demographics. By 2019 half of the children 18 and under will be minorities as defined by the USG. Each cohort that turns 18 every year will be more minority and more Dem.