In fact, I think a week quarantine is a terrible idea!
We actually don't have a problem at all with the wrong people posting. More precisely, the "wrong sort of questions" are dealt with quickly, and in most cases politely and appropriately. The moderation powers distributed amongst the users are more than sufficient to deal with this, we just need to continually work on civility and helpfulness (me especially, sometimes). Much of that work happens here on meta, as we all try to explain to each other what we think is going on, and what should be done better. A lot also goes on via email (as you can see from the fact that both Will and I corresponded with people over email in regards this one post!).
Even if we did have a problem, a week quarantine would be a horrible solution. It's really important to mathoverflow that there are no barriers to participation: a mathematician can hear about mathoverflow, load it up, and jump right in. We're really excited about this, and there are lots of features in the software encouraging this (e.g. we're happy that you don't even need to register to post!).
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