I have had a Cannondale Cyclocross Disc for about 10 years now and just upgraded to a Specialized Roubaix Expert Disc. Both of these bikes are used for a 15 mile (one way) commute to work on pretty rough pavement. I love the performance and ease of disc brakes and am not going to go back to rim brakes.
When I went to pick up the Roubaix, I rode it down the block and thought, "Wow, these disc brakes suck!" They had maybe an eighth the power of the Avid BB5s on my C-Dale. Then it dawned on me that they were not yet bedded in. I have changed out my pads in cars, mountain bikes and my C-Dale, and all needed to properly bed in to get proper performance out of them.
This will happen normally within a week or so of riding, but you can also speed up the process by riding down a hill and apply significant pressure on the brakes to heat them up. Do this several times in a row. I like to go to a steeply tiered parking garage and run several trips down at speed.
If replacing pads, make SURE you clean your rotors first. Any contaminates on your rotors will bake into your pads and decrease your stopping power. Just google "bedding in disc brakes" and you will see lots of tips on this.
I am now back to easily doing nose wheelies with perfect modulation on the Roubaix. Things are great as expected.
I am posting this for those who may be test riding a new bike with disc brakes. If you feel that, "disc brakes suck!" because they feel like they don't have any power, just be aware of this. As disc brake road bikes are just starting to come to market with popularity, sales staff should advise this to buyers.
If you still feel, "disc brakes suck!" on a road bike for other reasons, well then just enjoy your rim brakes.