In the worst case, you could destroy your phone. But 99% of the time, if anything goes wrong, you can restore.
Everyone sees jailbreaking differently. Some people cannot live without 3rd party apps. But I can't stand jailbreaking because every time I do it (I've done it 11 times) my phone starts freezing up and becomes really unstable.
If you are to jailbreak your phone here are some of the few apps I like:
- Sketches: Sketches is like an Etch-s-Sketch, but allows you to take photos
and trace them, use different backgrounds to draw on, use different colors and sizes, and export your drawing to the camera roll.
- Customize: By far my favorite app. Customize is exactly what it says it is: it allows you to customize you phone. With it you can change your carrier logo, the color of your SMS bubbles, your slider images, etc.
If you have Firmware 1.0.2 or previous, you'll have to use one of the methods that is done via an application on your computer. But if you have firmware 1.1.1, go
here and you'll be able to jailbreak right from Safari. (On your iPhone.)