I am an audiobook junkie, and once I realized that when I borrowed audiobooks from my local library via Overdrive.com’s software and transferred the titles to my 120GB Zune, they never expired. That was wonderful -- I have a library of dozens and dozens and dozens of books on my Zune. (OK, I've also had an Audible.com subscription for many years, and so I've got that giant library, too.)
Now if only battery life will make some quantum leaps in the cell phone world -- I'd be happy to use my phone for everything. It just slurps up the juice too fast at this point.