It would also help if they prompted for permission at the end of users' sessions, not at the start. No relaunch necessary and users don't have to wait for an update to install before they can start browsing.
Nagging people while they're trying to do stuff obviously isn't ideal either. So as just about everyone has mentioned: Chrome's silent updates are a big win for convenience. Because should the average user really have to think about keeping their software up to date?