I have been sorta considering getting a bike with disc brakes and it seems like from reviews alot of people end up wanting to replace the stock brakes of some of the cheaper bikes with BB7s or something better. I would read reviews of the bikes and maybe even just read reviews of the specific disc brakes on the bikes. Just something to keep in mind if you go that route since disc brakes are not a cheap upgrade.
Of all the bikes I like the look of the Felt becasue it comes ready as a commuter and the Trek PDX just looks cool, but its probably just the bars and position of them.