My car was produced in July of 2009 and I was able to load the maps from the USB port.
I have one tip to pass on that I haven't seen mentioned. If you happen to have an external hard drive with a USB interface, you can use that instead of a flash drive. You just have to make sure that the drive is formatted for FAT32 before loading the NAV files to it. I used an old backup drive to do mine instead of buying a new flash drive and it worked like a charm.
2009 335xi Le Mans Blue; JB4 - Map 5; VSRF DPs, VSRF Intercooler
LED interior, Angel Eyes, Glossy Black Grill
Rear Fog Light Mod; 2013 Nav. Maps