Incidentally I have a load of these (very inexpensive):
http://www.bluenext.co.uk/bluetooth-products/gps/92-bn-903s-gps-dongle.html
They are detected as a "cp210x: v0.09:Silicon Labs CP210x RS232
serial adaptor driver". Some googling suggests this is a USB2
chipset?
Sadly, as esr has found out, the cp210x linux driver is very poor and
gets no love from the vendor. It does not support basic ioctl() calls
that gpsd needs to utilize the PPS signal. So until there is a good
driver for them they are not an option for gpsd users.