It's already over 9000 so its doing ok
On a more serious note: it depends on many factors. I wonder how hard Sony will push it next year. If they give it a second chance as they did with the PSP/3, I could see it selling anywhere from 30-50 million. If they dont.... well it could always cap out at 10 million.
At the moment its not a struggle just for instal base, but for software sales to. Even tough there is absolutely ZERO piracy on it, the attach ratio is still incredibly small. Never the less I would hold out for a more reliable prediction at least a year, or even better, until we pass the launch the PS4.
Vote the Mayor for Mayor!