What people don't seem to get about both Quora and Google+ is that they are networks not based around the people you just randomly happen to know - but instead around the people and things that you are actually interested in. There's a huge difference between the two.
They are interest-based social networks and are essentially pulling niche, technical, specific forums, specific blogs, and just general chatter into one mainstream and real time feed - away from the pseudonym driven, trolling, harsh, fractured, and separate niche areas that we currently have in many areas (Yes I know both Twitter/YouTube began like this - but they have slowly become things you put on your business card/real business use and are based upon).
Quora should not be underestimated as a SV centric bubbletastic startup - although it often appears that way. But then again, so did Facebook, Twitter, Blogger, and even YouTube.
Quora is where you go to hang out with people who actually share your interests (and not just a zip code), talk about the things that you really care about (not about who was the most drunk on the weekend) and just generally talk shop about the world, with the added benefit of a centralized repository where content bubbles up everyday (kind of like YouTube's subscriptions feature). No more refreshing pages :D.
Quora is like the Hacker News for everything else that doesn't already have its own Hacker News with really, really, freaking good UI, addictive game mechanics and really good content filtering.
Quora should not be underestimated. And neither should Google+.