I save all my boxes, but the Apple boxes I have are the following:
20" iMac
30GB 5G iPod
15GB 3G iPod
512MB Refurbished Shuffle
Universal Dock
Shuffle Sport Case
Shuffle Dock
Jaguar
Panther x2
Tiger
Final Cut Express
Final Cut Express HD
iLife 04
iLife 05
Yeah I keep all my Apple boxes. The MBP box is nice and slim; I had it open on a chair in the corner of my lounge and on iChat recently someone caught sight of it in my background and thought I'd been eating a huge pizza
I kept them all, until the house and garage overflowed with them. Now I keep them, but I throw out the oldest box whenever I get a new one. So I maintain a steady state for the number of boxes, and I still have boxes for the newest items in case they need to be transported.
When my 2-year-old iMac needed a trip to the Apple Store (it got lonely to see its old pals there), having the box still around was very handy.
I've only kept the boxes for my laptops. I've found the desktop onces just take up too much damn space. Kudos to Apple for shrinking the size of the boxes for the MBs and MBPs although one might argue that the computer no longer has as much shock protection as a result.