The reason I recommend Chrome to all my non-techie friends is due to its automatic upgrades. I can be reasonably sure that my friend would be using a modern secure browser at all times.
Every time Chrome auto-updates itself, I notice it because it exposes some new "fit and finish" bug.
The update to Chrome 7, for example, broke the Bookmark Manager if you have your font size increased - e.g. due to eyesight issues. The update to 7.0.517.44 (or maybe an earlier version? I have no idea) changed the word boundaries used when selecting text using the keyboard.
It's frustrating.
I always thought a "upgrade Firefox on next restart" checkbox which downloaded in the background and kicked off the installer on browser shutdown would be nice.