I am just curious why the windowsphone.stackexchange.com still running as beta version. When it will be a release candidate?
When, if ever, a Stack Exchange site graduates from beta is a more complex issue than the Area 51 dashboard might imply. Simply getting an "Okay" or better in the five categories listed there is no guarantee of graduating.
Stack Exchange sites graduate when they've reached a certain level of maturity, including a self-sustaining community with enough high-rep users to moderate the site, and a healthy amount of incoming traffic (ideally mostly from search engines). A graduation-ready site is also expected to show maintained growth in user and post count with no sign of stopping.
For more information, see When Will My Site Graduate?
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The site gets a good number of visitors, but it doesn't get very many questions asked per day. http://area51.stackexchange.com/proposals/20757/windows-phone
I think the site would move out of beta if that metric was to improve.