I\'m developing an app for my company and we\'re going through the process of slowly letting people into the \"beta\" by adding their iPads to the company\'s iOS Dev Center
If any of your users are running linux they can use this from a terminal:
lsusb -v 2> /dev/null | grep -e "Apple Inc" -A 2
This gets the all the information for your connected usb devices and prints lines with "Apple Inc" including the next 2 lines.
The result looks like this:
iManufacturer 1 Apple Inc.
iProduct 2 iPad
iSerial 3 7ddf32e17a6ac5ce04a8ecbf782ca509...
This has worked for me on iOS5 -> iOS7, I haven’t tried on any iOS4 devices though.
IMO this is faster then any Win/Mac/Browser solution I have found and requires no "software" installation.