I've still got 2 Dell Mini 9's running! 1 with a black cover running win 7 Professional and another with a white cover running Mac OSx.
Both had thier hard drives die (but they areover 3 years old!) and i simply replaced them with Runcore Pro IV 16GB's and i couldn't live without them!
My gf has an ipad, but since you can't install office and the apps available are quite limited to be able to work efficiently, the dell mini allows that extra functionality when required. (without spending a hilarious amount of money!) and since everything is synced by icloud it works perfectly.
I still use my win 7 one quite regularly, it always comes with me if i'm travelling and will the full office suite 2010, skype and dropbox installed, it's perfect for buisness.
As i work in IT, it's also the perfect server room machine, easily light enough for 1 hand, and small enough to rest on anything, armed with a USB to serial cable it's perfect.
Also having a Network port with lights is important and awesome for such a cheap machine!
That armed with 3 USB's, the VGA port, the webcam, the 3G, the weight, the size and the fact it's silent, the fact it's much more functional than a tablet (full OS's) means there isn't really anything to replace it with, so long live the mini 9!
I just wish dell would revive it with a faster processor and the ability to thrown in 4GB of memory, and possibly up the resolution a bit, but form factor wise it's awsome.
plus it runs doom just fine..