Actually, the key is the EULA (end user licence agreement), one that we always skip when installing something. If EULA states you can't use that software if you're living on a fifth floor and have a yellow cat called Dipsy, you can't legally use that software if you're living on 5th floor with your Dipsy. However, when buying proprietary stuff, you are legaly entitled to ask the sales person a display of EULA before you pay any money for it.
So if DMCA puts some silly clausules for DVDs and such, tough shit for the Americans. On the other hand, i am the owner of the intelectual property, licencing terms are up to me. If you are ok with them, buy the thing, if you aren't, well...nobody's putting the gun on your head and forcing you.
Look at it this way...you purchased a car. You're a mechanic craftsman, so you want to craft replacement parts in case your car goes bad after the warranty cycle. The law prohibits "reverse engineering" of some parts, so if you craft a replacement part based on the original part, you're breaking the law. However, it is for your own usage.
This law about "legal duplicates" is really weird issue. You see, back in the good'ol days you had a Super Nintendo and a cartridge. If that cartridge got broken, you aren't able to play the game you paid for. So you could have one backup cartridge, legally. However, empty carts were expensive, and the equipment for duplication was also very very expensive. People dumped the cartridgers into one file (ROM - a file which contains all program instructions from the cart), and placed it on the web for free download, but you needed to "click here to verify that you posess the original game and will only use this ROM file as a backup". Needless to say, you could lie about it, download the ROM, inject it into an emulator or program an emtpy cart with it, and have a game without paying for it.
That was because the law didn't specify who get's to make a backup copy.
So they changed the laws in many countries, now specifically stating that you need to make the backup on your own, thus putting ROM scene from grey zone to illegal zone.
Now, all this text aside, the thing "you can't legally make a backup copy" is just industry bullying little people. You see, if you purchased Rock In Rio DVD, and the original disc got scrached beyond repair, if you can't have a legal copy, you'd need to buy the DVD again, thus giving money to the industry again. Which is total bullying.
I have an original Somewhere In Time vinyl. I transferred that vinyl into a digital form. I wanted to preserve the thing, because i don't have a 1000 euro record player, and i want to have the authenic vinyl feel while listening the stuff from my computer or the portable player. I didn't get a "usage licence" saying that i can only listen the stuff on the record player.
So aside the state law, and inside the moral laws, you are damn entitled to make a backup copy. And you're also entitled to make modifications for personal use. I mean, you can't reverse enginner an application, but if you do, let's say that you change the menu strings, you're using the thing you paid for in your own quarters, so what the f***? It would be morally wrong to resell modified things or spread them for free.
So, IMHO, make copies for your own use, for any kind of reason.