It took Google’s shares 52 weeks to move from $400 to $500. It took another 46 weeks to get from $500 to $600.

The next hundred bucks? A shade over three weeks, by the look of things. The stock was less than a dime away from $700 at one point on Tuesday.

Sure, those $100 hurdles get easier to jump the bigger you get (the latest one "only" represents a 17 per cent rise.) However, this now officially ranks as Wall Street’s biggest bout of Google-phoria in a couple of years: the stock has climbed by 40 per cent in less than three months.

You can put this one down to a classic blend of hope and reality. The reality is that Google is pulling even further ahead of its rivals. Who would have predicted that a couple of years ago, when Microsoft and Yahoo set out in hot pursuit with their own search plans? The hope comes from Google’s new mobile strategy, which is expected to be unveiled within weeks.

A familiar pattern is evident here. Google’s core business just gets better and better, but Google’s promising new businesses remain just that – all promise. The entire mobile advertising market is worth barely $1bn a year. As with social networking, there are valid concerns about whether users will take to advertising in this medium, and in what form. This is best seen as a long-term bet. But when you have the twin-engine cash machine of AdWords and AdSense to get you through the short term, will anybody care?

Larry Sanger is still predicting big things for Citizendium, the expert-moderated alternative to the "open" encyclopedia Wikipedia that he launched a year ago (we wrote about the launch here, and the implications of the Citizendium v Wikipedia battle here.)

Given the scale of his ambition, the results so far are decidedly modest: 3,300 articles, growing at the rate of 14 a day, compared to more than 2m on the English-language version of Wikipedia. Still, Sanger, who was in at the beginning of Wikipedia, is unabashed, as his update today demonstrates:

At some point, possibly very soon, the Citizendium will grow explosively–say, quadruple the number of its active contributors, or even grow by an order of magnitude.  And it will experience that growth over the course of a month or two, and its growth will continue to accelerate from that higher rate.

Comments like that make it sound like Sanger is succumbing to wishful thinking in his efforts to hit back at old nemesis Jimmy Wales of Wikipedia. Still, he has a point in one regard. Projects like this are deeply viral, and many of the experts he wants to attract will only jump in once they feel a tipping point has been reached.

As Wikipedia’s extraordinary expansion continues, I for one hope Sanger gets the formula right. It’s way too early in the development of the internet to hand so much influence over what passes for human knowledge to a single, still largely experimental website like Wikipedia.