I bought a Dynamic 7 speed drive mostly out of curiosity and because I like to try different things, and as a backup commuter.
I have 2 Gary Fisher mountain bikes, full suspension and hard tail, a Downtube folder S-A 8, a Strida, a Trek Soho belt drive, and an A-bike (don't ask).

The Trek has been my main commuter bike for almost 2 years but it's been in the shop a lot, squeaky belt that took forever for them to figure out. In and out while they tried different things, finally replaced the entire back wheel.
I bought the shafty to use while they figured out the belt issues. So 6 weeks of commuting on it, roughly about 135 miles a week, and here's what I think.

The Shimano 7 is nice, it's very evenly spaced gears, much more so than the 8. However it's low end is too high and it's tough on hills. On the Soho 8 there's a few hills I do in 1 and it's a bear on the 7 speed.

The ride is fine, it's immediate when you pedal, pretty much like the belt. In the beginning it did seem just a tad more sluggish which is probably a combination of the shaft, internal gear hub and suspension fork. I don't much notice it anymore but when I get back on the Soho it does feel a little zippier.
Getting out of the saddle and climbing hard has no apparent impact on the shaft. I can't say the same for the belt as I've had it skip (or whatever the hail it's doing) more than a few times. So far the shaft is rock solid.

There is a bit of a hum as you pedal, not annoying in any way, but you can hear it when there's no traffic around.

Weight is not an issue for me. I figure I'm out there to exercise and if I'm hauling a few extra pounds I'm getting more of a workout. Plus I carry a lot of crap, extra tools for removing the rear wheel on the Soho, a heavy lock, clothes, and I'm always stopping at the store and filling up my panniers, so I don't care much about it and thus can't really comment on it. I'm not running any races.

Rear wheel removal is one helluva lot easier than on the Soho.

The shafty I bought is $400 less than the Soho so it's not a really fair comparison when it comes to the other stuff, so I won't.

Longest ride so far was 42 miles a few Sundays back.

For now, I'm switching back to the Soho mostly because of the hills, but I plan to give it another good workout through the winter months to see how it does.