I've found this to work pretty well in most cases, but there are some websites that don't semantically mark up their fields in a way the browser can recognize, and there's no way to manually trigger the password suggestion feature.
My Thai business banking system is paranoid and disables autocomplete, paste, etc, even with the security of a physical token), but the one that really annoys me is things like Basecamp - I had to futz around and disable JavaScript for a login to be recognised and prompt to save a password - by default it does an XHR which doesn't trigger the "save password" prompt.