A lot of the problems arise because people use the same passwords (sometimes with the same usernames) on many different sites. So, for example, the fact that Sony has just lost over 70 million PSP account details might not be directly important to most of those people but if they log into their bank accounts with the same passwords they could find that they've got problems.
I'm also surprised at how many people have the same username on lots of forums (and other sites) on the internet. I'll sometimes Google an AB member's username, just to see if they're posting elsewhere on the net. (It doesn't work with 'AutomaticGal'. I've just tried!). I've quite often found out loads about people on here, including addresses and phone numbers, simply by following a few links. I'm not a stalker (I'm just naturally curious) but if I can do it so can many other people who know their way around the internet.
Chris