I have a Jailbroke 3GS now that I use with my ipad. Will the Jailbreak that was done on the ipad work on the new iphone?
It will be a while before 4.0 can be jailbroken. But don't worry there always is a way.
No it won't.
I give it a few weeks or less.
Personally, I'm hoping for a hacked carrier file that enables tethering. It seems that would be a lot quicker and easier to produce than a full-on jailbreak for the new OS.