From my perspective, pros are that it is low maintenance, you can shift gears at a stop light (that's major!), and it gives the bike a nice streamlined look. Cons are smaller gear range and/or bigger steps between gears. I commuted on a 3 speed IGH for a year or so in NYC and it was totally adequate for getting over the bridges and such. I did crave more gears and eventually got a 5 speed hub, but I never got to use that one much as it malfunctioned a lot--so by the time I got it fixed under warranty, I was not really riding that bike much and ended up selling it.

Anyway, are they adequate? Totally. Will you crave more gears? Only you know. I would think a 7 speed IGH would be a sweet spot for commuting.