It may depend on your riding style and the type of commute you have. I have an IGH, and I love it. My commute is 6-8 miles (10+ km) one way, urban riding, lots of stop and go. I love being able to shift into a lower gear from a stand still. I use a Nuvinci, so finding the right gear ratio is also not an issue, but if you're worried about weight, Nuvinci is the heaviest of the bunch.

I also ride an old 3-speed bike. There I can see where a cadence-minded person might have trouble finding the right gear. That's not how I ride, though, so it works out okay for me. But then I damaged my hub and have been single-speeding it until I get the new wheel built, and that has not been as bad as I feared, either. I suspect if you're terribly worried about keeping just the right cadence, then any sacrifice in your gear steps is going to hurt, but otherwise you can probably find a hub that suits your needs.

IGHs definitely have a rep for being more weather proof, so it's especially useful if you'r riding rain or shine. Maintenence seems easier and less frequent since most of the parts are protected. I think generally there is only one point of adjustment (if that) and most hubs make that pretty straightforward. In comparison I can sometimes fiddle for a while with my rear derrailleur trying to stop it from skipping a gear.

I just don't know about efficiency. It comes up a lot in IGH discussions, but I can't tell if it's really a practical consideration or just theoretical. I've used IGHs and I've used cassettes. I've never really thought, "Woah, this feels really efficient!" (or inefficient). I can't see that being a factor in my purchases, but it may be something that another rider would notice and be put off by.

I've done both. I'm not a speed-minded, or cadence-minded person (which is not to say an IGH prevents you from going fast). And I ride primarily in the city. My main ride is now IGH, my secondary ride is going to be an IGH bike (again) soon, and I'm building up a little folder, which will also have an IGH. Your situation/needs may be different, but if not, you might at least try one. With most bikes you should be able to swap it for a derailleur set-up if it's not to your liking, and a pre-built IGH wheel will probably fetch a decent price on eBay.