For web sites that have username/password text input fields, the browser usually handily offers to remember them for you (in my case, Safari puts them in my OS X keychain).
This simply does not happen with certain web sites. The first example that comes to mind is vBulletin forums. Meaning you can’t use a complex/random password unless you’re willing to copy and paste it from somewhere each time.
Are browsers detecting when to offer to remember these by “does this look like a username/password” heuristics and failing sometimes?
How does this work behind the scenes?
Edit: Fellow Safari users, check out this combo:
There’s an ‘autocomplete=”off”‘ attribute on form (not officially in HTML4, but generally supported).