Anybody can install 4.1 on their iPhone now, the GM is not locked to a dev account. This is 100% true. If you should drop or break or something else goes wrong your iPhone during the time between now and the public release of ios4.1 you will have voided your warranty by installing this GM. Although it may be the same build as the public release, it is not official software, so the warranty is technically voided.
Apples instore software will identify it as a GM. Even developers cannot bring a device into a store if something fails during the first year of its life, if the software is developer only. Same rule, void is warranted.
BUT, if you install this and you feel you will not be making a trip to an Apple Store for any issues then this is great! Install it. Next week you can download the new file and use iTunes to update in the same way you installed is GM.
This will make it 'official software' and thus warranty is restored to the device, providing all the other rules are observed.
Pheeeewwwwwwwww!