That is the ONLY good thing to come from Valves peice of "we rule the world" software; STEAM.
Once you have set up your Steam Profile, THEY know what games you have paid for. (Valve games that is).
So even if you're half life CD goes belly up, it doesn't matter. Log into your steam account and download the games you have paid for.
Of course if you have dail up, even this is not a good point and so Steam remains in my "what a peice of steaming......" book. (and I have ADSL).
As for cracks, I would agree that backing up SHOULD be legal, TOTALLY. However downloading cracks does put you at risk of porn pop-ups, add ware, and/or virus's

simple because to get them you are forced into the "underground" of the internet.
Unfortuanatly, if the games producers made the disks easy to copy, the industry would have an even harder battle against priracy which is a shame.
The person that said "meh, I dont even own the games" is not alone, but ask yourself this. Would you walk into a shop, pick the game off the shelf, and walk out without paying? Pirating games by burning them at home and downloading a crack is EXACTLY the same! It's stealing.
It was hard, but I did recently bin all my copied games.
You know how at the end of a game there is a really impressive credits list with loads and loads of people involved? Call them selfish, but they kind of like getting paid for the great job they do. MEH?
Anyway, all that said, your question can only be answered by researching the LAW in your country.
If you are asking "is it legal" then anything that is "opinion" isn't worth anything.
If you are asking "is it morally acceptable?" then that is diferent.