Well several years ago I purchased a 300D. I was happy and then I found POTN. Soon I wanted more, and you are at fault. Yes you! I then got an XT. It gave me more features. But I wanted more, its all your fault. Then I got a 5D. Man I love the 5D. So of course you know what's next. I recently started looking at the 1D series. Its all your fault, yes you!
There is pro AF with better support of f2.8 and above lenses. At a recent conference I got to use a 1DMIII, Wow! I feel like I have a target on my forehead, and the 1D is pointed right at me. Now I've found out that 1D has both exposure and flash metering in the viewfinder. I have rocketed my learning and now I want more. I want a 5D with Pro AF, etc or a 1DMIII.
In short the more I move up, the more the camera sings in my hands. Due in part to you. Aren't you ashamed of yourself?
Recently I've even learned to do paths and extract in photoshop. Yes some consider me a noob. But I can see the I am going to continue to move forward. Its all your fault.
How else hates/loves POTN. Even thought its costly and stretches us?


Second, determine what focal length you need. There are hardly that many overlaps in the L lens series. So, once you buy the right one with the right focal length, there is little reason to get another L lens, unless you are drastically changing the subject of interest (such as from portrait to bird photography). Finally, learn to take good, tack sharp pictures that pop. In this way, you will be satisfy with your existing L lens and would find no need to get another one. 

