It's been in Sept before, a few times, and once in Jan when the Sept one was cancelled because of a hurricane.

When it's in Seattle, it's usually Nov because of costs. Seems that's a cheap time to hold an event. This year in Charlotte is earlier.

I suspect 2014 will be back in Seattle.

Note that there are lots of fall events now. SQL Intersection (Paul and Kim of SQLskills run this) and DevConnections are both in Vegas. The end and start of Oct, respectively.

There's also SQL Server Live in Florida in Nov or Dev.

If you are planning out, SQLBits in the UK is usually the spring and a great event as well.