I would certainly recommend using the UNO or earlier revision with the socketed AVR.
Then you can have a couple of spare ATmega328's for backup.
You can certainly have AVR applications that cost less than $20, but there is a fair amount of cost in producing a development board. (You say $30 but there are plenty of sub-$20 Arduino clones.)
You can't do that with, for example, the Raspberry PI or the Netduino.
Method #10: Exceed Total Microcontroller Current
I'd imagine it would just temporarily disable it, but disconnecting the extra draw would put things right again... I don't think undervoltage or undercurrent physically damages the AVR?
So yes, it's definitely possible to damage a microcontroller in this way, but I'm not convinced it's as easy as the article suggests. (I'd try on an ATtiny right now and see, but my stash is at work.)
I'd not have been surprised to see "apply 120V AC to Vin/Vcc" on this list, simply for the common sense involved in such a statement.
All I can say is that once, while programming one of these ATMegas, I accidentally swapped VDD and GND and left it there for 2/3 minutes. The chip got very hot and I burnt my finger but once I left the chip cool I was able to program it again and after 2 years it is still working.
I know this one isn't true, because I did this last night with no ill effect. I accidently connected a 9V power brick with the leads reversed. Nothing happened, the Arduino just doesn't turn on until you reverse the leads.
One of the best electronic lessons i've read for a long time. Finally makes you realize why most pcbs has all those weird components sitting around instead of just pushing the io-pins straight into the µC.
While the avr might be able to handle some of the failures in certain scenarios it's still good to know how to protect yourself in case you use another controller or if you really want to be on the safe side.
