Moved to iPhone Jailbreak.
The pros outweigh the cons, IMO. Voiding the warranty doesn't even need to be factored in. You can restore to factory settings if you need to take it in for warranty work. Most of the problems and hassles you hear about are related to unlocking. Since you're already on AT&T or Verizon, you don't need to worry about preserving the baseband to remain unlockable, so the process will be far easier.
Jailbreaking is really easy to do. Some of the jailbreak tools only take a couple minutes. You'll always want to go with an untethered jailbreak. Tethered jailbreaks require a computer to boot. All major iOS updates have untethered jailbreaks, but you'll need to skip some of the smaller ones, such as 4.3.5, to retain an untethed jailbreak. Sometimes the firmware update is nothing more than a patch for the vulnerability that allows the jailbreak on the previous version. You can have the best of both worlds by staying on the older version and keeping your untethered jailbreak while patching the exploit through Cydia. It's fine to restore from a backup that was created on a jailbroken device.
Cons:
1. A teensy, tiny bit of lag. It's usually not even noticed unless you're using an older iPhone model. I notice that stock apps take about 1 second longer to open, but that's about it.
2. Battery life might be slightly decreased.
3. You can't hit that update button in iTunes the second it appears. Well, you can, but you'll temporarily lose your untethered jailbreak, so it's best to wait. If you do this anyway and then decide you want to roll back the firmware, you can do that as long as you have your SHSH saved. They are automatically saved after the first one.
Pros (There are a lot more than this. These are just some of the highlights):
1. The freedom to do things outside the scope of an application and the ability to install apps that were not approved for the App Store for various reasons.
2. Fast access to settings toggles.
3. Full access to the file system.
4. Customization and theming.
5. Custom gestures and buttons for features, such as a springboard pinch to activate the flashlight.
6. Managing photos and videos on the iPhone (create folders without iTunes).
7. Enhancing stock apps. Add a download manager to Safari, save attachments in email, add a download feature to YouTube, pull to refresh Safari, access WiFi only apps, such as FaceTime, on 3G, and add a navigate button to Maps (opens in Navigon or TomTom).
8. Live weather on the lockscreen and springboard.
9. Accelerate animations in the GUI.
10. Add more folder options and improve the task switcher.
11. Enable iOS direct printing (AirPrint) for non-supported printers.
12. Bluetooth media file transfers between iDevices.
13. Better text messaging apps. Send and reply to texts on the lock screen and from within apps.
14. Action Menu customizations. This adds additional functions, such as favorites, dial, and to bottom, to the stock cut, copy and paste functionality.
15. Add a user agent faker toggle so you can quickly switch between mobile and full site website browser user agents.
16. Free tethering.
17. Managing music without iTunes.