My two cents is that for pure road riding, be it racing or club riding centuries etc, discs are overkill and don't offer any real advantages to offset their penalties in weight, aerodynamics, swapability, need for a beefier fork/frame etc.

The road riding I'm thinking of, you are traveling relatively unloaded (just a basic tool kit and a snack or whatever) and you are trying to cover a lot of ground relatively quickly. The route or event or race is chosen to be enjoyable and minimize stopping. So bike paths / lanes, lightly trafficed country roads, side roads etc. I can't imagine how my ride on a nice nimble fork/frame with a well put together Campy gruppo would be improved by disc brakes. My calipers are easy to set up and adjust and offer plenty of modulation and stopping power. I don't feel under-equipped in the braking area. They are light, simple and elegant. If need be they can be adjusted / serviced on the roadside with a few basic tools. The rim, as others have mentioned, is a disc, so I already have disc brakes. I am supremely unconcerned about my rims wearing out. By the time that happens I'll be ready for a wheel upgrade. I can't imagine pro riders being well served by disc brakes, but I suppose if the component builders tweak and pay them enough some will do it. They want these things on the podium so they can start selling volumes to the wannabes. It would be nice if they recognized that, hey rim calipers for pure road riding are the apex, so lets just leave it at that. There's room in the component range for multiple options.

I'm not anti-disc brake. I have one on my Xtracycle, which is a cargo bike that I haul my kids around in my urban environment. Fully loaded the rig might weigh over 350 lbs. Believe me, I'm glad of the extra stopping power and more importantly much reduced brake fade that discs offer for this set up. Weight and aerodynamic penalties mean nothing in this application. Beefier fork? Sure, sounds great!

My urban / rain commuter is an older steel mountain bike (no suspension) with a sturdy rack and panniers. I run cantilever brakes with no problems or concerns, but if I was in the market for a new urban / commuter style bicycle, I'd seriously consider discs and that's probably mainly what I'd be offered. Disc brakes make sense in this application for same reasons as they do for my Xtracycle. I can see the advantages when traveling fully loaded in the rain on busy urban streets, with gritty slush to grind into your braking surface with the constant stopping and dumbasses in cars cutting you off and dooring you etc. Again, weight and aero probably don't mean much in this application.

The commuter bike travels to and from your home through the urban environment so keeping disc brakes serviced and adjusted is not a big deal. You can do it in your home garage or stop at a bike shop along the way. However if I was doing loaded or adventure touring, I'd go with rim brakes. Yes the bike is heavier than a pure road bike and maybe you don't care as much about weight and aero in that application, but simplicity and ease of roadside servicing should be of concern. Plus you are generally trying to get away from the crowded urban environment to the wide open road so you're doing less braking.

I haven't mountain biked in a long time, but I can understand the supremacy of disc brakes in that application, 'nuff said.

I have gotten into cyclocross, and I'm riding rim brakes (v-brake front, canti rear) and I feel well served. I see a fair amount of disc brake equipped 'cross bikes, but I don't feel at a disadvantage. Plenty of elite riders use rim brakes. 'Crossing is done lightly loaded (nothing but the rider really) and at relatively slow speeds what with all the twisties, run-ups and mud. You are never trying to stop, only slow going into corners etc. I'll keep my lighter rim brakes thanks. Also in 'cross you're constantly dismounting and even shouldering the bike, and I'd rather not have a pair of sharp edged circular saws on my bike to contend with. The wheel swappability issue is also a concern.

To summarize, I think it's a "horses for courses" subject and for pure road riding rim brakes still win. Light, simple, aero. In applications like cargo bikes and mountain bikes it's hard to argue with the advantages of disc brakes (mainly fade resistance) and the disadvantages are non-issues. In others applications like commuting and general urban riding I could see it being a toss up, based on the rider's specific environment and preferences. Personally I'd rather ride rim brakes for 'cross but others feel differently.