My 3G is my first foray into the dark side after MANY years of Smartphones. It does many things better, some not as good. Overall, I like the 3G. Jailbreak lets you add lots of applications on the iPhone that aren't available from the App Store. I'm driving from Vegas to a little town south of Tucson tomorrow and want my xGPS back (voice turn-by-turn). It's better than the Google Maps in that respect.
That said, if you walk into a store to get your phone worked on, a jailbroke phone will get them excited, and no warranty. iTunes "restore" puts the phone back to stock and they will take care of your problem.
First of all welcome to the iPhone world. Jailbreaking will void your warranty if Apple somehow finds out it was installed. If u ever have a problem and feel the need to take it to Apple, just make sure u restore back to stock. The only downside I find against jailbreaking is the lag of booting up and opening of apps. Sometimes what takes a second to open up can take about 3-5 when jailbroken. But you'll enjoy all the features of what's included in Cydia. Enjoy!