I've known Thomas for nearly 10 years and, like Thomas, I am a long-time Canon photographer. My first Canon was the brilliant AE-1, a 35mm SLR film camera that could take the full range of Canon EF lenses. I bought that camera in 1976. In 1988 I purchased Canon's first autofocus SLR, an EOS 35mm film camera that had model numbers such as the 620 or 650. Up until 2005, my main camera was Canon's outstanding EOS 3 35mm film camera. My first venture into full-feature DSLRs came with the the half-frame EOS 10D in 2003, followed by the 20D in 2004. I got the original EOS 5D full-frame DSLR in 2005 and that purchase took me into the realm of the superb L-series of Canon fluorite lenses and a whole new universe of possibilities.
Like Thomas, I rely heavily on DSLR technology, particularly the Canon EOS 5D Mark III. This is my main camera for "serious" photography. There are Nikon and other equivalents, but no substitute for this level of technology. I choose cameras for suitability to purpose. Unlike Thomas, I shoot primarily to describe rather than interpret artistically, but good description demands absolute clarity, speed and balance. You get that with a powerful combination of lens and camera technology and you pointedly do not get it with point-and-shoot substitutes -- and NEVER with mobile phones. I have never been tempted in any way to lighten my load with a lightweight substitute that cannot do what a full-feature, full-frame DSLR will do with a series of superb lenses.
This is not to say that lighter cameras do not have a place in my pack. I've become quite fond of Leica's superb series of new technology cameras. I carry a Leica T701 as a new-feature half-frame SLR when I want to carry something lighter than the EOS 5D Mark III. Leica lenses are superb and their cameras' processing technology state-of-the-art. My "pocket" camera is a Leica D-Lux 6, a half-frame fixed lens camera that is quite amazing for a camera of its type and size.
When traveling (something I do quite a bit), I typically take one of several ThinkTank shoulder camera bags. I am usually moving in crowded spaces and don't have the luxury of carrying or manipulating a backpack, so shoulder is the way to go. Even though I prefer to carry a series of superb prime lenses, practicality dictates that I work mainly with a very good zoom lens, and the Canon EF 24-105 f/4 L-series lens is my workhorse. My complement usually includes a 15-35mm f/2.8 L-series wide-angel lens and the same 50mm f/1.2 L-series that Thomas carries. I love the fisheye 8-15mm lens that Thomas uses and carry it just for fun. I don't have the 135mm lens that Thomas uses very often, but do have a 200mm prime that serves many of the same purposes; it's new so I haven't really gotten a role for it yet. I don't usually travel with the 100mm macro that Thomas uses, but I do have it for use around my home area.
There are all kinds of reasons to carry a serious camera if you are serious about photography. I have a strictly personal reason for a start. I am 90% blind, so I need a lot of technology to make up for an extraordinary deficit. Even if you have normal sight, there is nothing that will substitute for the speed, flexibility and clarity of a full-frame, full-feature DSLR with a responsive and extremely sharp lens. I try to choose my camera with the mission in mind. If I know that I need flexibility and power, I'll carry the EOS 5D Mark III to ensure that I can get the pictures I want. I have never been disappointed in making this choice. However, if I really do need to save the weight and give myself a lower profile, I'll carry the Leica T701 DLSR or, when I really want to go light, the Leica D-Lux 6. Incidentally, there are circumstances when you need another solution. Sports events such as major league baseball present their own challenges. Most MLB clubs will not let you bring anything that looks too professional into the stadium, so my solution is to carry a Canon Rebel 450 half-frame DSLR with a 24-200mm lens that gives me the equivalent of up to 400mm of zoom; no one ever suspects this 2008-vintage consumer DSLR to be professional and it does a superb job with the sports photography.