I have some information for you on why clerks don't check IDs...because customers don't like it.
I am a cashier, and at my store cashiers are required to match signatures. Now, this doesn't mean that 100% of us do it 100% of the time, but I think it is pretty close. You would not believe the complaints we get. We ask for ID if the card is not signed, if the sigs. don't match, or if "check ID" is written on the back. You would think that we asked for a firstborn child sometimes. Some people carry only a credit card, nothing else. Some people don't carry a state-issued ID, for whatever reason. Some people are too much in a hurry to show ID. Once a guy accused me of being racist, because I told him I needed to verify his signature. Some people give their credit card to their spouse/child/sibling/fiance, whatever, and expect us to allow them to purchase. How are we supposed to know that this person is really who they say?
The first step in avoiding fraud is to take responsibility for yourself...sign the back of your card and write "CHECK ID" in dark letters. This obviously won't stop all kinds of fraud...and won't help for online purchases or gas stations...but it's a start. Don't give your card to others...get them their own card! When you sign your name for purchases, sign it like you did on your card. Don't be in a hurry and just write your initials or a squiggle. If none of your signatures look the same, it will be hard to prove the ones that really aren't yours!
And about the "swiping" the card twice...sometimes we really do need to do that...without a hidden laptop to steal numbers. Sometimes registers don't connect on the first try. I'm not sure how you can avoid that, or tell if a criminal is ringing you up.
Sorry for the long rant/response...I just got home from work...long night!