I think that from the 3GS to the 4S there is plenty of reasons to upgrade, BUT if you are happy with your 3GS and are able to wait another year then why not? the iphone will only get better so waiting wont do any harm at all unless you cant wait have a look at the 4S features and think are these features something I will even use?
Not sure why you put this in the submit iphone news section though, Thread Moved.
I think the short list of reasons to upgrade from an iPhone 3GS to a 4S is not well documented. Going from an iPhone 4 to an iPhone 4S is reasonably well understood. Primarily the reasons are Siri, a better camera and a more powerful processor.
But you have to also look at what features of iOS 5 will you not receive on your 3GS. I have not yet seen a well-defined list to date. There is an older article from 9to5Mac but it's 4 months old and refers to iOS5 beta 1. Even a search on YouTube doesn't come up with much.
IMO, the best way to consider it is this.... the hardware features of the phone dictate where the software can go. The hardware is the enabler. If you are a casual user and don't play games and photos are just for the rare snapshot moment, then wait. There's always something new and interesting later.
While many obsess about the lack of external changes to the phone (not a bigger screen, not slimmer, etc.), I'm more interested in the interior of the device. Upgrading the internal RAM of the device is likely to be a very big deal. That newer processor is also going to be impressive. I'm personally looking forward to what my iPhone 4S looks like when connected to my TV via my Apple TV2. That's going to open up a whole new realm of games and applications. All those people who have been looking for apps for the Apple TV2 are going to have their hands full now.
I only ever play games when im bored. I dont play them very much. Im on the internet most of the time on my phone like facebook and youtube and other internet sites. I LOVE taking photos and editing them and i think that the whole idea of the siri is so good for me. I lisiting to music all the time. Ie that good?
If that's the case, then it would seem that the improved camera will be a big improvement for you and that the improved processor is probably less of a draw for you. However, it was identified in iOS 5 beta 1 that the image editing features that are new to iOS 5 will not be available on the older 3GS handset, so that is an additional incentive for you to upgrade as well.
Since games are not a big part of your usage, you probably won't notice the better graphics processing, though the overall quickness should be improved a bit. However, you certainly should appreciate the higher screen resolution that was introduced with the iPhone 4 and continues with the 4S.
In short, you could get by for another year without the iPhone 4S. If you feel like changing your carrier within the next 12 months, then upgrading would be a bad idea. Some people really want LTE and so they might want to wait for the next handset next year on a different carrier.
But I think it's very safe to say that there are enough upgrades and enhancements over the last two years to justify upgrading from a 3GS to 4S.