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.

Sounds awesome. I take it you can still climb the hills by going to 1st and stand-up mashing?

Yeah, can still get up the hills no problem, it's just harder. My morning commute is much more uphill and, since half the time I'm not awake, I sometimes like to take it easy on those climbs and just settle in. Harder to do with the Shimano 7.

They come with the Nexus 8 and Alfine but I really didn't want to put that kind of money into something that is primarily a backup (and a curiosity).

Standing on the pedals and mashing is probably not a good idea with this shaft drive bike. I have about 4000 miles on a Dynamic (with 8-speed) and I have never had any problems. But if you do push too hard, you drive the grease out of the bottom bracket gears and you will hear gears grinding. A few shots of grease will fix this - in fact any time you hear gear noise, give it a shot of grease thru' the Zerk fitting. After 4000 miles my bottom bracket is full of grease and rarely needs any more.
Standing and pedaling is not good for hub gears either, and there is no easy fix.
M Riley