Security of USB dongles/data cards
"Probably the only security issue with mobile broadband is loss or theft of the USB dongle or data card, and with it a user’s access credentials."
There is no user stored data on USB dongles/data cards - the users access credentials (which are generic anyway, unless you are using a private APN) are stored on the laptop.
Some dongles now act as a memory card reader as well, so the only risk would be if you had a memory card in the dongle and then had it lost/stolen.
Also, it's worth remembering that you don't necessarily need a dongle/data card to connect your computer to to the cellular network. I get my laptop online on the move by connecting it over WiFi to my phone. The advantage of this is that it gives me "unlimited" data at no extra cost. I use an iPhone with the PdaNet application to do this.