I suspect this is an "unofficial" leak directly from LG. In reality, I personally believe LG leaked this to see how it went when hard core users like us would update the phones vs. trying to go beta with it and causing major issues with G2x owners that weren't allowed to participate in the beta.
I updated my phone last night and it is working far better then it had been... it is faster and no issues so far. The funny part is that I have a "replacement" phone coming today. I am going to refuse delivery and send it back. My understanding is that the refurbs and "replacement" phones aren't taking the update. If this update were officially coming from LG or T-Mobile you would get it OTA not via the update tool. That is unless it is too large a file to go OTA. I also believe T-Mobile would have announced the update. Even the LG web site doesn't have it listed as a download. So leak it is.. but it is a good one!
To be frank I was going to accept the replacement (which would have been #3), keep it for 30 days and send it back to fulfill my 3 phone requirement before being allowed to go with another phone. I then would have gone with the Sensation... but now I hear the Sensation is having some major issues. So why go thru the trouble if this leaked GB update has fixed my G2x... which I think is the best phone out there.
The real problem lies with the carriers and manufacturers turning out new phones every other day. They are just moving way to fast and not putting the proper amount of R & D into the phones like they used to. So we, the consumer, end up with phones that don't operate properly because the software is faulty or the software doesn't work with the hardware the way it should... on and on. LG, HTC and Motorola need to slow down and take a breath. Enough new phones for a while!