We had a chance to talk to the people responsible for USB 3.0. The new standard will let you have 5Gbit/s and in an ideal world that would mean 625 MB/s.
The draft is out and the first version will again be copper based, while the optical version might come at later date.
According to a chap involved in creating the standard, the first devices will come in late 2008 and he thinks that USB 3.0 can attack standards such as eSATA and at the same time it won't bring much to your printer.
Prototypes of USB 3.0 cables and controllers are expected early next year and retail devices might follow by the end of next year.