I'm not sure if its been mentioned as of yet, but the new iOS firmware has an 'unremovable' watermark so Apple technicians can see if you've Jailbroken your phone.
If you have, they will tell you to get stuffed and not help you so your warranty is void.
I know we don't have the new iOS firmware yet but I would imagine most of you will want it, so get rid of your JB before you set it up etc.
I'd say its not really a risk worth taking for the time being.
Yeh i heard about this so will wait a bit to see if its true or not and whether the jailbreakers can find a way to disable the watermark or bypass it.