I think it has a niche. Personally, I don't see it competing with Facebook because it's not as simple for "out of the box" simple status updates. It's a typical Google product in that it's very customizable but, in the case of a social networking platform, that takes away from its usability and simplicity.
It's great for sharing pictures, especially if you have an Android phone or tablet. Techies (like myself) love it, we don't find the lack of simplicity off-putting and appreciate the ability to have control over what we do. It seems like barefoot/minimalist runners for some reason have made a home over there (not sure the connection but most of the people in my runners circle seem to be barefoot/minimalists).
Regardless, if you're there, so is HillRunner.com. If you're not, you can still find HillRunner.com on Facebook, Twitter, or of course right here.