I was recently asked to write an article on the subject and was hoping to get some ideas from the good folks here (as well as it possibly being helpful to some).
Here's a few to start:
1. What is Mastering?
2. Is Mastering Necessary?
3. Should I limit/normalize/compress my mixes?
4. What format should I send for mastering?
5. How much will it cost?
6. Which is better analog or digital?
7. What is the best software for mastering?
8. What settings should I use for xyz?
9. Can a mastering engineer add reverb/delay/increase the level of a track (i.e. can the ME perform some forms of remixing).
10. How does that Tom guy at the MH stay so good looking day after day?