I've just returned from being incognito (hidden) on the forum, It was an experiment to see what it's all about, for me it was no different than being signed out except that I could still post, someone hidden here is basically a signed in guest the only difference being that they can post and do other stuff as regular members do, the less the better I think.
Also I have a super fantastic forum name and an exceptional quality avatar to go with it so hiding it would be well....unsightly.
Personally I tend to read the forum more often signed out and generally at night on the TV which bumps me off regularly anyway and only sign in if I am contributing
well adding stuff then, others have different needs to mine and overall I think it works well for my needs as is, if others have a requirement to become incognito then they have the option of becoming a supporter of the forum.
Like most things in life it's a paid subscription or an earned privilege as far as I am aware.
In regards to privacy on the forum I don' really have any concerns but I do keep regular tabs on the who's online list for no other reason than to see what the current popular topics are and then proceed, what I don't particularly like are zero post members running around with nothing better to do than look at and I presume read everyone else's profiles, I wont name names and have pointed this out to a moderator in the past, don't believe me then keep tabs on the list yourselves.
Members that have absolutely nothing to contribute should be purged on a regular basis, I don't even know why they are here.