Other Odds and Ends
The Nike+iPod feature is an interesting one and works just like the iPod software that you can get with the Nike transponder. This allows you to use your iPhone as a workout tool with a separately purchased sensor from Nike. It is great if you already have this and the shoes from Nike that you need, otherwise this iPhone 3GS only feature is of little use.
A couple of other nice features that come with the OS 3.0, but are not limited to the 3GS, are Apple's inclusion of Stereo Bluetooth support! - This feature is a long time coming and again, as with many (well, just about all) of the new things in the OS 3.0, should have been out with the first iPhone. I cannot tell you how many people I know who have been waiting for this one.
Additionally, there are slightly better parental controls available in the new OS and you can now limit quite a bit of the phones capabilities and even restrict the allowable content ratings for videos, TV and movies.
I do wish they would let you restrict things such as SMS and E-Mail, though. Or that there was a way to block everything and make the iPhone just a phone if you needed. But that is just my personal desire for the phone.