If you have the iPhone 4, then it is not worth upgrading to the iPhone 4S. It has all the iOS 5 features, but the only thing that the iPhone 4 doesn't have is the Siri voice assistant and is specifically for the iPhone 4S. If you really want the Siri voice assistant then go for it. But it's likely that the next generation iphone will have it as well.
Also who knows what Apple plans on doing. Their original release date for iphones is June/july. So it is likely that Apple may go back to their normal release dates for their next generation iphone, which is only like 9 month away. So I'd wait and find out. Even if they do decide that October will be the official release date in the future then I'd still wait till next year then.
IMHO, only You can decide whether to spend your money to upgrade from your current iPhone 4. I personally am not going to upgrade to the iPhone 4S, because I really don't need that 8 MP camera (I barely take pictures on my iphone), I don't need the 1080 p HD recording (I barely use my phone to record). A5 Chip isn't that interesting to me. Although it's dual core, iphone 4 (A4 chip is still fast enough) can still handle fast. Also a huge disappointment is that iPhone 4S still uses the 512 MB RAM, which isn't an upgrade at all. So I'm going to wait till their next generation iphone and see what it has and if it's worth upgrading then I'm going to upgrade to the next generation.
