Oh please yes, let it stay! :/
... what is the GM built?
- the final version?
do you know when this will be released?
and... will it cost again like the update to 3.0?
GM = Gold Master, its the term Apple uses for all software builds that are final and are to be released to the public. As for release date, no idea. Apple sometimes announces the dates, but most of the time its a highly guarded secret. As for cost, it should be free, at least all updates since 3.0 have been free as far as I can remember...