Not very well (especially Forerunner 201).
Here are a few undesirable effects that will happen if more than one user attempts to share a Forerunner:
Some of these issues might be negated on Forerunner 301 if each person uses a separate sport profile (e.g., running, biking, or other). History can then be separated, but there will still be some issues from shared weight and gender values in the user profile.
See Also