Hydraulic disk brakes typically have more lever travel before they engage.
Rim brakes can be adjusted so that the brake pads are very close to the rim resulting in very little lever travel before the pads actually touch the braking surface.
Disk brakes typically retract the pistons and pads so that it takes more lever travel to engage. This is especially true as the pads wear. Once the pads touch the rotor and the brakes engage however, disks brakes should feel every bit as good as rim brakes.
Personally, I like rim brakes adjusted with minimal lever travel, almost instant engagement, hair trigger. The extra lever travel before engagement is one thing I don't like about disks. It bothers me.
-Tim-