Things have stabilized a bit at ObamacareSignups.net, as some of the early speculative numbers are starting to settle down into actual, real-world figures.
As a result, as of today, the tally for people who are now covered by by health insurance who weren't prior to the launch of the Exchanges is only a bit higher than it was a few days ago (721,646 to be precise).
It's important to understand that sources and methodology for this sort of tracking is going to vary widely, depending on what exactly it is that you're trying to track (as well as the source, of course). In my case, yes, I'm including Medicaid expansion signups, because ultimately, what matters is people actually getting decent medical care at an affordable price.