For that last reason alone, you should install iOS 4.3. But there's more than just improved security in the latest upgrade: to additional apps, Safari now runs faster, iTunes Home Sharing is better integrated and personal hot spot support for the AT&T version of the iPhone has finally been rolled out.
Apple's iOS 4.3 is compatible with the iPhone 4 (the GSM model only), the iPhone 3GS, the third and fourth generations of the iPod Touch, and both the original iPad and . There's also a related AppleTV update for those who have the latest AppleTV, which was released last September. Not getting this update are the first- and second-generation iPhones, released in 2007 and 2008, and earlier versions of the iPod Touch.
In addition to the big changes offered in iOS 4.3, Apple tucked away several minor tweaks: the Camera app has a new shutter sound; the Notes app gets a few additional fonts; the Location Services setting is now prominently displayed under Settings; and Ping notifications are available.