We're now in the process of identifying questions that are:
- Recent (in the past three months)
- Unresolved (there's obviously a discussion still happening)
- Very Stack Overflow specific (retag, tag burnination, cleanup, etc)
We will be keeping a list of these, and migrating them back to MSO very soon after everything stabilizes. Note, this is going to be a very conservative list, we expect it to be between 50 and 100 questions in all.
After the split, if you think that we've missed something, flag it on MSE and let us know that you think it needs to be shipped back over to MSO. However, please do not flag just for the sake of bucketing or sorting content - unless it's very recent and seemingly unresolved, we'll probably decline.
A major requirement is to make sure that people keep as much of their rep on MSE as possible, so we're not inclined to pull questions about Stack Overflow that also relate to the network as whole. However, some of you might lose 50 - 100 rep from very recent questions or answers, unfortunately there's not much that we can do.
Beyond the very recent and unresolved questions, it's up to Stack Overflow to talk about the stuff that they want to talk about on their meta site - so the announcement is accurate, we're not going to be sending a lot of content back.
If you have additional questions about the split, use the support tag, along with the mso-mse-split tag. Please make sure to include the latter, as questions about this project will be quickly obsolete once it's completed and any remaining issues settled - at which point they'll be going away.
If you want to leave answers to this question with links to posts you feel should be shipped immediately after the split, please feel free to do so, just try to avoid duplication.