JailBreak Questions

I have the 3GS with OS 4. The trick to jailbreaking
is to make sure each app downloaded with cydia is working properly before proceding to another app.
Cydia allows for removal of apps with it's modify section.No functions of OS4 will change unless you want them to.I would say the risk is nill if you procede carefully and systematically.
If worse comes to worse you can still restore

 

You cannot brick a 3GS except for sudden hardware failure, which has nothing to do with firmware modifications.

Jailbreaking is easy and a 3GS can run jailbroken iOS 4 or 4.0.1 with no slowdown.

If you want a full list, best to start reading.

 

If you are already on 4.0.1 just point the safari browser on the phone to jailbreakme.com. Move the slider to the right and sit back and watch it happen.

After you finish the jailbreak you can secure the browser by going to Cydia and installing the PDF patch, this plugs the hold that the JB exploit uses.