Firstly, is there any chance we can have a story without someone using the word "bubble"? This is not evidence of a bubble. More to the point, it's a boring prediction because it doesn't add anything. Some years from now we may well be in a bubble and the person who happens to be right that day will say "See? I said we were in a bubble" and the previous 1000 days of being wrong will be summarily ignored.

Basically it's pointless.

As for Quora, I stand by my original assessment: I don't see this going mainstream. Q&A seems to be something that works well for particular verticals (eg programming aka Stackoverflow) but doesn't seem to be a general purpose or widespread tool. This is in part cultural (eg I believe Q&A is very big in Korea).

I see this more as "bubble thinking" and in this context "bubble" has nothing to do with valuation but more that the people who use and value Quora live inside a bubble. That bubble is the Valley. VCs and Valleywags only know other VCs and Valleywags and all of those people use Quora so they make the mistake of thinking it's far larger than it actually is.

Quora does not have the mainstream breakout appeal that, say, Pinterest or Instagram does and honestly I don't think it ever will (you can quote me on that). Neither does (or will) Stackexchange.

That's not to say either won't exit for 9-10 digits but that's another story entirely.

Quora has done a fantastic job of marketing itself to VCs/Valleywags but I see Q&A much like I do Foursquare and the whole check-in thing. It's a (to borrow a Mark Suster term) FNAC (feature not a company).

IMHO Quora will suffer the same fate every social/curation site does: eternal September. If it ever does grow massively the influx of new people will change the site and those early adopters people like to follow now will move on to the next thing. It's Slashdot, Digg, etc all over again.