After doing some recent research, I understand that the IMEI number is also stored in the handset's flash and is, from the provider's perspective, your handset's unique identifier. It is broadcast to the network thereby giving them the potential ability to bar (amongst other things) that handset from their network.
AFAIK, over here, Orange is the only provider to use this facility to network lock (as opposed to handset lock) stolen handsets. This is something of a missed opportunity but perhaps the other providers turn a blind eye to handset theft in return for call revenue but that's another matter entirely!

To circumvent these locks and to disguise stolen handsets, people re-write the flash and IMEI number using a cheap dongle cable and PC software. So, coming back to your question about showing the label with the IMEI number, I think it's potentially a bad idea.

Edit: Clarified network lock