I'm using Debian testing and I don't get the /dev/hiddevX file either. Instead I get /dev/usb/hiddevX. After creating a symlink in /dev and changing the permissions, everything appears to be working fine.
With a PN20 I can transfer waypoints and routes from the GPS to the computer and do real-time tracking. I will attempt to do some more thorough testing later this week or next.
2009-06-16 20:23:40 UTC in GPSBabel