This page explains the new truss design:
http://www.glguitars.com/features/neck.asp
Doesn't say anything about graphite but they've definitely revamped the process.
My most recent G&L bought about a year and a half ago still has the old bi-cut neck design, with the maple board sawed in half right down the middle of the fretboard, so I can't give you any sort of comparison of old vs. new.
As for quarter vs. flat sawn necks, I think all of the newer US models I've seen have been quarter sawn. Tributes appear to be flat sawn. Then again, it may be that the guys at the factory approach every piece of wood differently. Some harder examples of maple may lend themselves better to flat sawn necks since that method produces a more flexible neck. Pure speculation on my part. All I can say for sure is I got a new SB-2 neck under warranty at the same time I bought a new SB-2 and they both arrived quarter sawn.
As for ditching the bi-cut method, well, I never met a G&L neck I didn't like, however it was made, so I can only assume this new technology carries on that fine tradition of rock solidity.