For Surface, Microsoft made $908m in sales, but spent $839m to make the devices. Compare that to last year, when they sold $2.13b worth of Surface devices but spent $2.87b to make them.[1]

I wouldn't say it's a key profit area for them yet, and we also can't call it a success yet (as they haven't reported the total retail purchases).

[1] http://blogs.wsj.com/digits/2014/10/24/a-win-for-microsofts-...