The stock ICS is browser is the best stock Android browser to date, there's no doubt about that. However, it's not perfect - it's actually missing one crucial setting: UA string switching. On the other side of the table, it has a killer new feature (found in settings > labs) called quick controls. Once enabled, the URL bar will disappear, giving you more screen real estate for browsing. To access the settings menu, address bar, tab bar, etc., a simple tap on either side of the screen will bring up a circular menu with all of the options right there.
So, what does all this have to do with Browser Plus? These are the features that BP builds upon. It takes the stock ICS browser, adds the ability to change the UA string and brings navigation controls to the quick controls menu, making an already good browser even better.
To activate the extra quick controls, go to settings -> labs
To set the User Agent String, go to settings -> advanced
Grab Browser Plus from the Android Market today.