What makes Boot Key Harbor so attractive is that it is well-sheltered from nasty weather and is easily accessible from the Gulf and the Atlantic (via Hawk Channel). Spent Jan.-April there back in 2004, some time at
anchor outside the harbor, but the bulk of the time was spent on a private dock next to Burdine's Marina.
If you plan to spend some time in the Keys, you need access to a motor vehicle, or be prepared to walk or taxi. Stores are not close to one another and are deigned to serve the needs of shore-side residents, not cruisers. However, you can find just about anything you can possibly ask for within a 3-mile stretch.
Despite the distances involved to reach shopping, Marathon is probably one of the most cruiser-friendly towns in Florida.