On the web you can BumpIn to anyone

The concept behind BumpIn is sound enough, while surfing the web you can see other people who are on the same website. Thus allowing you to discover other people with similar interests, chat live with them, make new friends etc.
It's only been up and running for a short while now so doesn't have a very large userbase [yet] so many websites you visit won't show anyone else there (bummer).
Realistically you'd really need a widescreen monitor to make the most of this (as the browser add-on reserves a portion of your window for chatting and showing a list of related websites). So that excludes about half the web surfing population (again, bummer). Hopefully it will take off as it's a really cool concept :-) Failing that I'd love to see a future version of StumbleUpon incorporate its feature set as they've already got the requisite userbase.