[jacquesm]

I made a very early version of something like this in 2002 using a loophole that allowed me to frame content in such a way that the original site was visible in an iframe with avatars and speech balloons for the visitors floating over the iframe. Unfortunately the next release of the major browsers closed that loophole (because it could be used in bad ways just as easily as it could be used in good ways). That was a real bummer, I really liked the idea of 'meeting' people on other websites if you both visited through the portal.

Maybe with the current generation of browsers there is another way to achieve the same effect.

On websites with lots of visitors this would likely not work but then you might limit the visible entries to those from some slice through the population based on certain criteria (location or other demographic data).