Not directed at any one certain person, but I have to put my 2 cents in. Doesn't that border on paranoia, as to who is invisible, and who is not. There again, you have no idea what peoples reasons are.
I don't look at it as lurking, as much as a private thing!
Peoples reasons vary, and I bet that perhaps there should be a different word to use then "invisible".
oooooh, something mysterious, or erie about that word perhaps. Whatever their reasons, they perhaps don't care to be part of the crowd. I dunno. Interesting topic. Would like to hear more!

Sincerely,

SongBird