I agree we need a way for a user to hide their email if they want, but we should leave this important community
back channel open (e.g. a form that does not show the recipients email allowing them to ignore or respond to the sender that used the form). For an example of form based user contact option see a
Userland Manilla site (the mail includes useful things like referer info).
If you feel like getting deeper than a simple site wide on/off form option for email implement it in a way that allows levels of permission on the entire profile: e.g. I want my friends (and friends of friends) to see my entire profile (email included), but registered users and non-registered users to only see X,Y, and Z (with contact option over email limited to the form). For an example of different levels of view permission from a web based social networking site see orkut.com (which has permission level of profile based on relationship to user: friend, friend of a friend, strangers).
Now to make it even more interesting: with roles and different kinds of groups made possible by OpenACS it gets fun quickly (hypothetical example from .LRN: multifaceted student X wants to share certain parts of her profile with the pink commie hyper-liberal dissenter political student "club" she attends on Tuesdays and other parts of her profile with the young neo-conservative republican group she frequents Thursdays).
