I’ll update if I get any more info, or any kind of response from founder Arianna Huffington or her people. A source “close to the company” informs Silicon Alley Insider that the reports are “stupid and false” and “wrong across the board”; Huffpo cofounder Ken Lerer is an investor in SAI (see lengthy disclosure below).

That said, the size of the round and the valuation both sound plausible. And they reflect the rocket ride the site has been on for the past year or so (someone who should know better allowed the New York Times to float a $200 million estimate earlier this year, but no one takes that seriously).

ComScore pegged the site’s traffic at 4.5 million unique visitors in September 2008, up from 800,000 the year before. Meanwhile the DrudgeReport, the site’s conservative counterpart/model, was at two million. Both sites will claim their traffic is much higher, because that’s what every Web publisher says when confronted with outside numbers (this one included). But by any count, it has gotten very big very quickly.

The big question is whether Huffpo can sustain even a fraction of that growth rate in the aftermath of the election (and sell ads, too, though that’s another matter). Huffpo’s standard answer to that question is that that only 50 percent of its traffic comes from political stories. And indeed, there is plenty of real estate dedicated to topics like Lindsay Lohan’s love troubles, and those of Madonna, as well. And here’s a page called “Sex.” Guess what it’s about?

But there are lots of sites that can tell you about those topics–and indeed, Huffpo is primarily in the business of aggregating that stuff in an eye-catching way, not creating original content. And while the Huffpo people are absolute wizards at optimizing the site for search engines, and maniacally focused about tweaking the site in real time for optimal click-throughs, it really will be hard to sustain growth without political fervor.

If you had to bet on political Web sites that will grow for the next four years, you’d be better off placing a wager on sites that cater to conservatives/Republicans/etc. for the same reason that nonprofits of that ilk will raise more money during the same time–anger and frustration are great animators. Recall that conservative talk radio really exploded once Bill Clinton took office–and yes, this augurs well for Fox News, owned by News Corp. (NWS), which owns this Web site. (And while we’re at it, I most recently worked at Silicon Alley Insider, which has a loose distribution relationship with HuffPo. Phew.)

One hopeful note: New politics/stats/forecasting site 538.com, using an admittedly crude measurement, says both HuffPo and Drudge have been able to keep their post-election audiences.