1) Number 1 rule: Bike theft is a crime of opportunity 99% of the time. "Crime of opportunity" means that those that stole your bike weren't planning, tracking, and scheming on how to get your bike. They probably saw an unattended bike and went for it. To a theif, an unattended nice bike is like finding a $100 on the ground.
2) Crackhead theives like to steal bikes with names like "Trek" "Cannondale" etc... That's why some people de-badge their bikes to look like cheap bikes.
3) Crackheads will steal ANYTHING that they think they can sell for $20. Cocaine is a heluva drug.
4) No lock is 100% safe. Locks just buy time. A $20 cable lock will buy you about 5 seconds. A Kryptonite NY Fagidaboutit will by you about 15 minutes or much much less to a theif with the right tools.
5) An ounce of common sense goes a long way with you keeping your bike. Don't leave your bike unlocked while you "just run in for a second" to ANYWHERE.
6) Believe it or not, there are teams of theives that patrol major cities and college campuses in vans/trucks that steal 20+ bikes a night using pro tools. They then take them and sell them in other cities or online.
7) 99% of bystanders won't stop a theif if they see one stealing a bike either because they don't realize that it's being stolen or don't want to get involved.
8) Learn how to properly lock your bike. Locking a $1500 bike to a tree with a 2" trunk that can be snapped in two by a reasonably strong person isn't smart.
9) Thieves will take your bike from inside your house, apt, garage if it is unlocked.
10) Don't be surprised if your $80 Thomson post and your $150 Fizik seat are gone if you had just an allen bolt holding it on.
11) If they REALLY want your bike. They will get it sooner or later. Especially if you have a routine.
12) This is life in the big city. If you get caught slipping, you'll have to pay a "stupid tax".
13) Avoid locking your bike in a place were someone can work on your lock without being seen.
14) If you can, take your bike in with you to your job or whatever. Ask nicely.
15) Just because you live in a "nice neighborhood" doesn't mean people won't do dirt just for the hel of it. I know plenty of rich kids that steal for kicks.