Where do you lock up your bike? This is very important, and usually even more important than the bike lock itself. Any good lock-up is only as good as where and what you lock it up to. Never lock a bike to a small street sign pole that is easily un-boltable. Never lock it to a dummy pole (pole secured to a base with 1 bolt). Never lock it to a flimsy bike rack that is bolted together. And lastly, never lock it to a chain link fence. Basically if the thing that you are locking to can be fairly easily cut or unbolted then it is not good.
Years ago I had 2 of my bikes stolen right out of my locked up basement. That is when I learned to always lock up my bikes even when I have them stored at home. Keep the bikes away from where they can be seen through a window of a storage shed, garage, or basement. Another thing to always remember is to never leave a bike that is locked up unattended for a long period of time. If a thief has enough time, they can get through almost any kind of lock. No bike lock will ever be 100% secure. If a bike thrief sees 2 locked bikes, most likely he will go after the easier of the 2 to get.
Many may think that bike locks are more appropriate for commuter bikes in an urban environment. Even though bikes are more often stolen from urban environments, mountain bikes are also very commonly stolen too. Mountain bikes and their components are usually much more expensive and even more desirable to thieves. It really is sad to think that this kind of thing happens at all. I once saw at a bike park where there was a row of cars that had broken windows. They were parked at one of the more remote sections of the parking area, and a slew of expensive bikes were reported as stolen from them. I would suggest to park in an area where their cars would be more visible.
Internet and social networking: In this high tech world sometimes too much available information on the internet is not a good thing. Very detailed social networking information on Twitter, Facebook, Myspace, Strava, etc… of what kind of bike you have, how fast you are, how often you ride, what all your upgrades are, can sometimes be too much info. On another note, please be careful to NOT post GPS bike route information on the internet that can point a thief right back to your home or where you store your bike. Thieves have been known to use this info and then end up breaking into your garage or basement to get your high end bike.