Stever Robbins has some great Tips for Mastering E-mail Overload (via 43 Folders)
My first personal email peeve is getting CC'd on irrelevant emails. It is especially prevalent at organizations where individuals and groups lack clear duties and responsibilities. It results in people who don't (or won't) own a problem, and who really just want to share their responsibility (with you!). I generally write back and ask specifically why I was copied on the email, and what I am expected to now do.
My second email peeve is receiving meeting requests that don't state (in writing) a clear purpose and expected outcome for the meeting. It's amazing how many meetings either become more effective, or are found to not be required, simply by clearly answering those two questions in advance.
See Also: 43 Folders: Five fast email productivity tips | 43 Folders: Quick tips on processing your email inbox