Rough estimates are one thing, but hard data on Xbox Live arcade sales has been pretty hard to come by. Until now, that is. A pair of talks at Microsoft's XNA GameFest show just how successful Microsoft's foray into digital delivery has been.

The first talk, by Microsoft casual games manager Marc Whitten, revealed that Microsoft expects 45 million individual game downloads on Xbox Live Arcade by the end of the year. Developers have made $30 million in revenue on XBLA games so far, Whitten said, with an average game returning 156 percent of the initial investment within a year. Try getting that from a mutual fund.

That's fine for the business in general, but how are individual games doing. XBLA Platform Manager Mark Coates stepped in to help answer that question with a series of slides showing the most popular games available on the service. The data varies widely depending on what metric is used -- while the Ninja Turtles arcade game has the most individual users, Street Fighter II HD has made the most revenue and Uno, of all things has the most minutes spent playing. Coates' presentation also showed the longevity of XBLA games -- 65 percent of an average game's sales come after the first two months -- and the continued growth in download rates (see above graph)

Remember, all these numbers come despite the fact that 30 percent of Xbox 360 owners don't even know that Xbox Live Arcade exists. Imagine how high the numbers could go if more users knew they didn't have to go to the store for their 360 games anymore.

[Via GameSetWatch]

Read - Marc Whitten on the XBLA business
Read - Mark Coates on XBLA game rankings