I have the Sanyo dynamo hub, which might be even heavier than the Shimano. It's one of the cheapest dynamo hubs. I absolutely love it. I agree with others above. I don't feel it unless I'm feeling for weight.

If you haven't felt the freedom of dynamo lighting yet, you are going to love it. There's nothing to check or think about. Just jump on the bike and go! Not only does it work from one day to the next, it works from one year to the next. It just keeps on going, no matter what the weather or anything.