With my recent question issue (see Where did this question go wrong?) it seems like a nice feature for users would be to auto suggest the correct site for a question. This could happen any number of ways, but I would think a quick and dirty implementation would use the tags the user has decided to use.
For example, my question was apparently better suited for workplace. I used the people-management tag. If people management type of questions are not suitable for P.SE it would have been helpful (since I didn't know about workplace initially) for P.SE to suggest, "Hey, you're using a tag that might make your question off-topic for this site. Maybe XYZ would be a better choice?".
Just my thoughts. I realize it could be a huge job, but could help new users and anyone who isn't familiar with the 50 SE sites that are available.