Where to start! Well lets go ahead and discuss the significant upgrades to this iPhone:
You notice the minor speed difference when dropping to an iPhone 4 and even more when dropping to a 3GS. I notice the speed difference but its not as significant when going to an iPhone 4 but its a god send when coming from a 3GS. If you use photo apps and so on that process through then the iPhone 4s is worth the upgrade for the speed. The speed is even more evident when it comes to the camera app where speed increases and certain features have been added thanks to the A5 chip.
The camera is has some significantly better color presentation and resolve but more so the speed is simply so useful when it comes to opening the camera app up. I barely use other apps for the initial photo, I tend to use them for editing later though so this speed up on the native camera app is seriously welcome. More so add in iOS5s tweak of the lock screen, allowing for one to take pictures via the lock screen it and it's the perfect point and shoot!
This is a pretty dicey subject since some people get more others less and so on. The truth of it is that this is very much on how you use your phone. I've found that when I initially got it I managed to get in some cases between 1 hour down to 30 minutes of use per 10%. So in total I could get either 10 hours or 5 hours, really on the days that I was testing I managed to get somewhere near 7 hours in total. I wasn't using 3G like crazy since the 3G constant usage is aimed at 8 hours in which case I decided to do the re-calibration move. This is essentially when you drive the battery to zero and then charge it, this is meant to reset the battery and allow the phone to properly understand the true battery level. At least this is the explication offered to me by an Apple Genius bar guy. The other thing he did note was that it's best to do this once every month or even every 3 months.
After doing this I managed to achieve a good amount of usage from a single charge. Close to 12 hours and still 30% charge but this was using the phone sparingly. When using it heavy I was left with 10% after 12 hours which is still good enough to get through a normal day. The difference seems to come also with the amount of time spent using Siri and the Internet on 3G. Long story short, if you love the Internet and use it a lot or have apps like Siri that use the Internet. Make sure you have WiFi if your going to be making any heavy use of the Internet.
Wow. This is probably a feature I wish they threw in instead of FaceTime in the last iPhone because it gets more use then FaceTime ever did. More than that though it's actually, like most reviewers have said, made me make use of the calendar and reminders app more than I ever have before. The sad thing is here in the UK it isn't fully functional yet but from what is functioning its doing an amazing job. The minor complaints from most people here in the UK I've found is that the man who is playing the role of Siri is rather annoying and that they wish they had the American version which sounded a little less posh and ridiculous. I don't really have this issue personally since I use the Australian setting which has a Sheila (Aussie for 'girl') as the voice. Siri is still in beta and so I do forgive it but it does tend to be quite annoying when it messes up multiple times in a row. This I'm sure will improve over time. It isn't so much that they are piloting this but I feel as if they are looking to get as much data into the Apple servers to constantly improve and bring the voice recognition up to speed before they throw it into every device where even then the Apple servers may be finding it hard to keep up. I say that because there have been a few times where Siri seems to have had an outage and other times it has difficulty connecting even when signal strength is full and on 3G. This will be no doubt an amazing advancement and although Android has a similar app I believe, I doubt their team is as big and as dedicated as Apples simply because this is going to be a major product on its own in many ways. Unlike their other apps I see this one evolving constantly and have found that names it previously found hard to understand it started coming around to. I also found that its best to keep the mic dead in front of you rather that to the side just so Siri can hear appropriately. It doesn't do so well in areas with a lot of noise but I have managed to use it to make a phone call or two even then. It's brilliant for the cold days since I can reply and sort things with my voice rather then removing gloves and adjusting manually.
This is majorly improved, I find that the 3GS is still the best iPhone for signal though in many cases, having friends who have them and seem to get signal when I don't but once outside there is no problem what's so ever or even near a window. The other thing is that trying to do the 'death grip' as before is unlikely to cause the drop as it once did. I'd say it's pretty much solved but I'm sure the next iPhone will have as good if not better signal then any iPhone before it and they'll probably be pointing that out.
It's a 4.5/5 simply because I feel my iPhone 4 got better battery life thanks to the ability to run on Edge rather than 3G but this is a minor point. Siri is worth the upgrade alone and so is the camera and the better signal (if you had the death grip issue before). Its comes back as my favorite phone even more thanks to iOS5. Now if only everyone would trade in their blackberries for iPhones to use iMessage. Its probably a less than significant iPhone update if you take away the Siri but its still an awesome update. Highly recommend upgrading if you have the ability to especially if your still running anything less than an iPhone 4.