Right now, if you have a modern, reasonably fast machine and don't have a touch screen... not much of one.

If you have a touch screen, it does a lot more with it than Win7 does (assuming you have driver support.) It's also faster for some things, although it's only going to be noticeably if you have a marginally usable older machine (or if you reboot a whole lot; I don't get the obsession with boot times, but the speed-up makes some folks happy.)

If the $30 upgrade is time limited, I'd consider picking it up, just as I'd recommend to people buying a new machine to get Win8Pro and then downgrade: in a couple of years, as more software is written to require 8, you'll probably want the option to upgrade to it the, and the full retail cost of the upgrade makes a cheap upgrade now worth hedging your bets on.