Here's my garmin mounting cradle for the nuvi 550.
You can see how there's a holder for the mini (or micro?) USB power cable.
It's nice to have a holder if you aren't taking a gps, like when you're just commuting to work.
Also, the area where the cable plugs into the gps device is covered a bit, which is good for the rain. The nuvi 500/550 are waterproof, of course.
I went ahead and put some dielectric grease on the plug.
This is better than the cradle from RAM. That cradle doesn't have the plug holder and cover. Just FYI!!