I have read quite recently that the "next generation" SATA drives rated at 300(as opposed to the currently 150 speed rating)are due out sometime soon or maybe it'll be the middle of next year.

Does anyone know anything about this?

Well I did post a thread on the coming SATA II drives here:
http://www.pcguide.com/vb/showthread.php?t=37053&highlight=SATA+II

Also found a Hitatchi review here:
http://www.bigbruin.com/reviews05/hitachi7k500/index.php?file=1

Also a review on Hitatchi, Western Digital, and Samsung:
http://www.anandtech.com/storage/showdoc.aspx?i=2454

Also there is a naming change, now being called SATA300 vs SATA150 for the WD Raptor type of drive.

SATA drives have no good performance if you just use them with old chipset.
You can get some information from www.sata.com;there is whitepapre for your ref.