Off the back of this question, is it true that the u-blox GPS can only receive either GNSS or Glonass but not both simultaneously? I ask as that's what the documentation for the chip suggests and it would be nice to have both - presumably the Rpi is only interested in an NMEA data stream, so it would be a matter of the correct driver.
I'd quite like to use my (self-powered) Dual GPS160 over bluetooth, but I suspect that, with the myriad different GPS units out there, support might turn into a nightmare!