Ok dude. I owned the Samsung Vibrant, which is the Tmo Edition of the phone. For starters, Swype can be downloaded to any android phone, so don't worry about losing that, and the screen brightness, you should worry about losing that since that's a Samsung Design.
Now about the customization, I'm guessing this is your first smartphone? LoL!! Sorry to be so shrewd about that.
About the update things, what doesn't update?
Force closes on "certain apps" as in the-apps-that-you-downloaded-from-the-market-and-are-not-the-legit-Google-applications? I'm guessing you don't know this, but apps are different from iPhone to Android. With Android, I can easily open an account with Google for $25 and then post my App to the App Market. Just like that. It's that easy.
Its good for getting many different apps, but then that leaves a whole lot of room for error apps. I'm guessing since Apple only uses certain developers, you get less errors. As with Google, you can't have as high as a guarantee that the app "will" work.
A lot of people complain about battery life, but what are you coming from? If you are leaving a phone that had the 9 number buttons, then yes, you will complain about battery life. LoL!! I remember you used to be able go 2 days without charging your phone. Newer smartphones use more energy, and if you can go a whole day and make it back home with some battery left, you have good battery life. But if you only can get 5- hours, then yea, unless you're like always downloading something and I do mean always.
Your Yahoo mail not updating, the reason being, I think it's because it's not a normal email account. When you connect your Yahoo, it tells you that some Yahoo Mail accounts won't work. That alone tells you, you may have some issues with your Yahoo.
Try:
Open up your Yahoo inbox using the Email App
While in your inbox (not in an actual email, just the inbox) press "Menu"
You should see (Refresh, Compose, Folders, Accounts, Account Settings)
Go to Account Settings
You should see something that says (Email check Frequency)
Right there it tells you how often it checks for your Yahoo email. I guess you can see what's going on. You might have it on -Never- since the latest option is -1 Hour-
Freezing phone? Oh no!! Quit opening apps back to back. LoL!! I'm guessing you're doing that. I had that issue to. My phone would start to slow down. After being on for a while. Just like a computer. Slowing down after being on for so long. I guess your phone is low on RAM and the easiest way to fix that is restarting. This can not be avoided neither. It's actually mentioned that a way to keep your phone running at optimal speed is to shut it down at least 1-2 times a day. Like a computer, when the RAM gets low, things start slowing down. If the phone can't keep up, it usually just turns off on its own. That's what my phone's been doing lately, but it happens when I go from App to app without letting them close. Playing games and having the music playing at the same time after I had just left the market to download a cool app, which triggered my auto-update for my apps, so I'm now downloading and installing 10 apps.
And I guess your phone turning off when charging is proving my point above. You're getting low on RAM and your phone turns off since it knows you're not going to reset it. LoL!! IDK...
Sorry it's so wordy, but I just wanted to give you some depth since you was thinking about getting the iPhone with it's lack of customization features. -_-
But if all else fails, think about this. You can still buy your iPhone 4. Early termination fees are about $200+ and I think you have to return the phone. Starting a new contract with a smartphone is probably going to be $200. So that's $400 you apparently have. Since AT&T uses SIM cards, you can sell your Captivate for $300, telling people you did't want it, and then just buy the iPhone 4 and put your SIM card into that. That's what I do with Tmo. I hated the HD2 so I sold it for $300, and got a new phone for $200 instead of $500+tax. LoL!!