Nexus 7 on our Motus behaves very well. As Nealh says, change of gear when stopped is a big benefit. (In fact, we chose the hub version after my wife got caught during a test ride on a derailleur in high gear after a pause at the bottom of a hill; restarting was very awkward.)
Downsides:
It does need a complete stop of pedalling for 1/4 second or so to change gear, just backing off pedal pressure doesn't seem to be enough. Easy and not enough to lose momentum on a hill, but something extra to have to think about.
Gear range is much less than a typical derailleur system. Plenty on a crank drive with adequate motor. I wouldn't want the Nexus 7 on our tandem with (underpowered for a tandem) XF07; we often need a much lower gear then the Nexus would give with any reasonable chainring.
The Enlivio hub is also interesting, wide continuous range. I've never ridden one, and it too is much more than the Shimanos, though not nearly as much as a Rolhoff.