As Groupon pursues its plans for an IPO, it's proposed valuation keeps on going up. First it was $15 billion , now it's $25 billion , according to a report by Bloomberg. Remember, it was only in January, 2011 that it closed a $950 million venture round at a valuation just shy of $5 billion . What's going on here? Is this yet one more sign of Internet valuations getting out of hand—dare I say the "B" word? One of Groupon's venture investors, Ben Horowitz of Andreessen Horowitz, doesn't think there is a bubble. At a press dinner last night in New York City, we were discussing valuations in general and he pointed out that Groupon is now doing "multiple billions of dollars in revenues." To be fair, Horowitz was in a roomful of bloggers and journalists trying to pin him down on a number and he was hemming and hawing, but he seemed to be referring to expected 2011 revenues. I take "multiple billions" of dollars to mean more than $2 billion , which was the annualized run-rate back in December. Compare that number with the $760 million in revenues for 2010 reported by the WSJ and you get a sense of its growth. Remember also that Groupon is only two years old. The faster the growth rate, the higher the valuation. But this isn't only about valuation, it's about ego. At $25 billion, a Groupon IPO would nudge Google to become the largest venture-backed IPO ever.