Most wedding planners (including myself) are asked this question: What's the difference between a wedding planner and a day-of-coordinator?
The Winter 2012 issue of Martha Stewart Weddings directly answered this question!
Acutally, they're all planners. but their roles change depending on what you hire them for. If you want help with pretty much everything-from setting a budget to sourcing favors-this is considered full-service planning. You'll need to bring someone on months in advance, and they'll work with you all the way up to the big day, which they'll spend finalizing last-minute details and troubleshooting unexpected problems.
If you'd like to handle most things yourself (DIY bride), but want someone to setp in when the date draws close, most planners also provide day-of services. In this situation, theyll come onboard a few weeks early. First, they'll wrap her head around the plans you've already made and create an itinerary for the day. Then, they'll become the point person for your vendors. Day-of, they'll be on-site to make sure people and objects are where they need to be.
*Did you know that I offer both services, but specialize in day-of coordination?!