I have two bikes, a road bike with a derailleur and what I'll call an all-purpose bike with an IGH.

The road bike features middle gears that are pretty closely spaced. On the Shimano 8 speed IGH there is a significant jump between 5th and 6th gear that bothers some people. I definitely notice it coming from my road bike. By using different sprocket/chainring combinations you can control where that 5 to 6 speed jump comes in to play to a certain extent.

Anyway, it's not the best option if you plan on using it for groups rides where you are trying to closely match speeds with a group of people. That really doesn't apply to commutes so it's not that big of a deal. I live with it.

On the plus side, if you get a newer high end Shimano IGH (red band, alfine) you'll be treated to an almost silent drivetrain even when coasting. No click,click,click,click noise as the wheel spins.

As far as weight is concerned I blew it when I converted my Bianchi to an IGH. I had weighed it before and after but lost the "before" measurement. I was curious as to how much difference it really made since you are getting rid of one chain ring, two derailleurs, one cassette/free hub, one shifter, and one cable. I'm guessing it's still heaver but even if not, it definitely puts more weight in the back.

One niggling concern is the use of grease as a lubricant in the 8 speed Shimano IGHs. It increases drag in cold weather. I get a double whammy because I'm also using a roller brake in the rear. I hope to swap my Nexus Red Band out with an Alfine and move to a disc brake instead. Pricey change but if I sell my Red Band wheel in the Spring I should recoup a good chunk of it.

Eventually I'd like to try an oil bath with the Alfine but probably won't do that the first winter.