I've had mine done last August by Antirouille Metropolitain. It is a MESS for the first 2 weeks (leaks and smell), but since I usually keep my cars 6 years and more it is worth to do every year.
I think it is a good idea if you only have one car and you live in an area where it snow a lot. Other than that, you don't have a whole lot to worry about.
I had it done by the dealer when purchased. Had to bargain it into the price of the car. if you live somewhere you may need it, try to get the dealer to through it in for free. I ended up with alot of neat stuff since i bought my car in november (a set of snow tires with rims, rust proofing and extra floor mats)
good idea, but definately dont drill holes. that leaves exposed metal (yes even though it would bt coated in fish oil etc) which is the worst thing you can do. you'd be best to just take off the inside of the doors and putting the hose spray thingie through the plastic.
dont forget a well kept car even without rust proofing will resist rust. my previous car was a 1978 holden ute (i live in australia - it's a aussie only car) and i REALLY looked after it. no rust. no rust proofing. i live by the sea. that's proof enough for me that looking after a car is worth it