Like me, Giles of Simple and Usable doesn't like the fussy new faux leather appearance for Apple's iCal and Address Book. He's created a new skin for iCal, and inspired by that, I've done the same for Address Book. To use it:
1. Make a copy of Address Book, in case something goes wrong.
2. Download this file (simply a compressed folder of .png files).
3. Quit Address Book.
3. Copy the contents of my file (all the .png files) into "/Applications/Address Book.app/Contents/Resources/"
If you need more detailed instructions, the process is very similar to that described at Simple and Usable
This is what it looks like.
Macnix has an easy to install silver skin for each of iCal and the Address Book. I've not tried them, but it looks like the Address Book skin leaves in place quite a lot of unnecessary shadows, faux "stitching" and so on. I've tried to remove as much of that as possible.
Edited to add: I've fixed the link above. Apple killed me.com, so I moved the file to my dropbox.com account. If you like this fix, please open a dropbox account with that link and I'll get a bit more free storage!