I don't really qualify because I use a car for long trips, night travel, going out with wife, etc., but I do use my motor bike for almost all my errands and day trips including getting all my groceries. I have ridden 2000 miles in 4 months.
The last few weeks I have used my motor bike for errands of 30, 40, and 50 miles. In fact, I love it when things are far away because it gives me a destination to ride to and new routes to explore. I live near Washington, DC and in the city and inner suburbs it is easy to find good routes. The outer suburbs are a challange because they are designed with a mixture of high speed highways and residential cul-de-sacs that go nowhere.
My bike is a good quality front-suspension mountain bike with a GEBE kit, a 32cc Tanaka motor, and a heavy-duty real wheel. I have ridden it for 2000 miles with no problems whatsoever.