Hans de Goede of Red Hat has been one of the developers who got the UAS driver support into shape for Linux 3.15. USB Attached SCSI is a protocol for USB HDDs / SSDs / flash drives that use the SCSI command set and generally allow for much faster transfer speeds than traditional USB mass storage drives. UAS was introduced with the USB 3.0 specification, but not all USB 3.0 rated drive enclosures, etc currently on the market have UAS support.
With the Linux 3.15 kernel the UAS driver should be in good shape along with XHCI streams support. I don't have any UAS drive enclosures right now for being able to benchmark the performance and support under Linux, but when I get my hands on such hardware, there will be USB Attached SCSI Linux tests on Phoronix.
With Linux 3.15 is also USB 3.0 bulk streams support from user-space using USBFS. With the upcoming QEMU 2.1 release, the USB 3 bulk streams support will be taken advantage of with its USB 3 redirection support to offer full USB 3.0 compatibility.
More details on these recent Linux USB support improvements can be found via Hans de Goede's blog.