That number's already been responded to.Wasn't it supposed to be already leveling off at about 20% ?
But if you look at the data regularly, you'll seen an interesting thing.
Every morning, there's a 5 to 10% rise in Yosemite adoption, and a corresponding fall in Mavericks. However, over the course of the day, the precipitate rise and fall disappear.
That tells you a couple things:
First: GoSquared is smoothing its data somehow; probably a simple moving average. That'll allow the end of a time series to swing wildly as the average includes fewer and fewer points.
Second: It seems a lot of people are trying Yosemite installs overnight, and rejecting the OS during the day. Else that morning spike would stay up, and we'd see a net adoption rate higher than the current ~0.3% per day.