My money says it behaves naughty when communicating with a Garmin USB device.
10.4.10 changed the way it handled bulk pipe stalls and hosed libusb which, in turn, hosed GPSBabel.
About a half dozen people reported this to the list just after 10.4.10 was released. I published a beta
that contains what *I think* is a fix to the problem. I published a
that asked specifically for
feedback on this. The Mac .dmg has now been downloaded
and I've even dropped a note to each of the original half dozen reporters asking if the beta returns joy to their lives. Nobody has reported success OR failure with Garmin/USB (or much of anything else) on the beta, so I'll be darned if I know if it actually works for anyone but me or not.
So I'm left to figure that with >2,000 downloads and the absence of complaining, it must be a Good Thing and should ship it. I'm also left to deduce that 1/3 of our users are Mac, six of them use USB Garmins (the most popular GPS on the planet) on the current version of Mac/OS and they all lost interest before the beta. That's statistically sound, right?