I can't really recommend any device, I don't have any myself. I just know quite a lot of people use the Garmin eTrex Vista series. That would also make sense for backpacking.

I can answer the software question though.
Garmin recently opened up a Mac OS X section on their website where you'll find all the information you need. They announced last week at MacWorld a new software specifically for Mac called Bobcat. Details are on the same page.
There's a number of other software for communicating between your Mac and your GPS, commercial or free/donationware (type in GPS as a keyword on MacUpdate or VersionTracker, you'll find the biggies like MacGPSPro and others). One of my favorites has to be TrailRunner. I don't have a GPS but I use TrailRunner to plan my routes, get elevation data, and generally trying to find new interesting routes to go to. It's got another interesting "diary" function in which one can save the routes cycled, total number of km and other whatnot. It handles GPX files so it works with pretty much any GSP out there I would guess.