The Source Sans Pro font is designed for GUI applications, and Source Code Pro is for code editors like Visual Studio or EditPad Pro. I have changed my browser's default monospaced font to Source Code Pro as well, and it is much more legible that Courier New, especially when it comes to similar characters like I, i, 1, L and l; or O, o and 0. Hopefully I'll spot a few bugs this way. I plan to use them for a while, until they either annoy me completely or I stop noticing them, and miss them when I'm working on someone else's computer.
They are also available as web fonts using Google Fonts or TypeKit.com, so they can easily be incorporated into web sites.
Update Friday 5 Oct: After a week of fiddling with various font settings, I have decided that Source Code Pro 10pt is too small, and 11pt is too big, but not by much. So for my 50-year-old eyesight I'm sticking with 11pt for now.