Now, I'm a pretty big fan of News Gothic and Helvetica Neue (got kind of burnt out on Myriad after it showed up as the first font in Adobe programs all the time). I've grown an appreciation for gothic typefaces and their restrained, solid aesthetics and function. And when I saw that Source Sans Pro was at least influenced by the gothic designs News Gothic and Franklin Gothic, I was excited. But what I was concerned about was that it was just going to be a generic Myriad knock-off. I was pleasantly surprised when I did the comparisons to quickly see that there was indeed a gothic influence when compared with the common Myriad.
The Source Sans Pro type family is definitely worth the free download...especially if you're looking to have a nice, functional alternative to some of those common system fonts. Plus it has more styles included in the package than those others.
Read the story behind the design (by Paul D. Hunt) here. Download the font package here.
(Note: All fonts in this comparison sheet image were set with auto kerning and auto leading in Adobe Illustrator.)