I've been loving my belt driven Norco Vesta (I've converted it from SS to Alfine 8 speed). The drivetrain is very clean compared to a chain setup from what I've seen thus far - the bike will see its first true winter conditions soon enough, which will be another true test of this.
The belt is very responsive - there is no input lag or stretch, and the feel at the pedals is quite nice.

As mentioned in other posts, belt alignment is crucial. If the rear wheel is not perfetly even in the dropouts (i.e. the rear cog has any angle off of perfectly square with the belt axis) then the belt can wander. It does appear that Gates has acknowledged and addressed this with the certer-trac system. I know as an early adopter of a new application that there will be tweaks, but I can report that I am an extremely satisfied belt user thus far.

As far as the IGH thing goes, try it before you write it off. The current Alfine 8 offers a very wide range that is comparable to most compact road (39/53) drivetrains with the exception of the top couple of gears.
Most 2 and 3 chainring drivetrains have many useless or redundant gear combinations. It is not uncommon for a 27 speed drivetrain to have 13-14 unique useful gears once the duplicates and "chainline limited" combinations are eliminated.

Hills? Bring 'em. My current setup offers a 28 inch first gear, and I've easily tackled 20% grades on and off road. Top end? I spin out at about 30-31 MPH, which is plenty fast enough for me (I'm not racing). If on a steep hill, I tend to coast anyway (again, my racing days are over).

The IGH tradeoff? Sure. The larger steps between gears means that fine tuning your pace in headwinds or on long grades is not as convenient as on a road bike with a close ratio cassette. The difference is less noticeable when compared to wider ratio cassettes.

The highly anticipated Alfine 11 will be a boon, as it offers better steps between gears with a larger jump to first gear for a great bailout.