I have encountered this problem yesterday (but only realized it today). I suspect it has to do with the sync feature in Chrome. In my case, I have been using Google Chrome for about 2 years, and it's even synced most recently with my iPod Touch and iPad 3. I've used a Win7 Laptop and Desktop, so that's 4 computers that share the synced data. It's a great feature.
I probably had close to 200 saved ids/passwords, with all the various stuff I used for home and work. On all of my Chrome instances, the data was gone (!). My girlfriend encountered the same problem, but she only has an HP Laptop.
There are more than a few complaints about this,
but I haven't found anything from the Chrome team that explains how it happens. Edit It's a bug in Chrome with iOS.
There are two possibilities: 1) the data got wiped from the Google server where the syncs are stored in the cloud (although my Bookmarks are still good across all the Chrome versions), or 2) one of the n Chrome instances uploaded empty (or corrupted) sync data, causing it to propagate to all my other Chrome instances.