The feature never really took off and even Facebook admitted defeat. Mark Zuckerberg acknowledged that "people don't like making lists." I will agree that they don't like making lists but I do think that like things to be grouped and organized. Sink or swim Google+ has solved the problem to getting your connections into their groupings. To add someone to your network you simply move their name into the respective circle (group).
One of the Achilles's heel of lists on Facebook was that there were too many steps. I had to friend someone and then I was able to go back in and put them in their correct list. Google circles takes care of that automatically not in the sense that it's picking the group for you, although I'm sure Google's working on that, but the action of adding a connection and grouping are one in the same.
Going against Facebook is no easy task though and Google has failed at social before. What puts Google in a good position however is number one they have multiple web properties to add customers from. Secondly it's helpful that there is differentiation between Google+ and Facebook. Rather than being just a direct competitor Google has done something different and it may pay of in the end.
The Diaspera project is proof that just being a Facebook alternative is not enough to hit "critical mass." Critical mass is the point in which enough users have adopted a social network to sustain it. Diaspera received millions of dollars in funding simply because it wasn't Facebook. Google+'s immediate popularity has been attributed to the fact that it's not Facebook but one of my favorite quotes is "It's like Facebook and Twitter got together and had a sexy baby."