It's a personal call, and I think all of the advice given so far, both pro and con, has been valid.

For me, the cost is worth it, especially as I was already building up new wheels for my touring bike. In that case, I rationalized the main investment as just being the difference in price between a Shimano generator hub and any other reasonably good hub -- not a huge premium, IMHO.

I rarely ride after dark, but I (sometimes) enjoy starting before dawn. And, I like to have my lights on in the daytime if it's raining or even just dreary. For that, dynamo powered lights are great.

When not powering lights, I use the dynamo to charge up a cache battery that I then use to power my USB-based devices: iPad, camera battery charger, and cell phone. That's largely for the novelty, though, because I stop in places for food, restrooms, etc. enough that I could probably keep the battery charged just by plugging in every time I had the opportunity -- even without relying on campsites.

So, if you want the most cost-effective way to keep you gadgets charged, I bet you could get by with just getting a USB backup battery from a cheap online supplier like Monoprice.com and getting into the habit of plugging that in every time you can get access to power. You could then use that to charge whichever devices have the greatest need once you're at camp.

EDIT: 58Kogswell posted his reply during the time it took me to write mine, hence some redundant information. He makes several good points, but one thing I'd like to add is that although it's true I've found direct charging of some devices from my power converter (an E-Werk in my case) to be problematic, all such problems went away once I got in the habit of storing energy in a USB cache battery and charging my devices from it.

My cache battery can store 10 Wh of energy, and I've found that to be just about the ideal capacity, as that's about the amount of energy I'm able to consistently store during a day of touring. I've bragged about this many times before, but I did a 4,600 mile tour during which I took lots of photos, called home each day and wrote a blog entry each night on an iPad in my tent, entirely with power from my dynamo hub -- I never plugged in. Here's the blog, if interested: http://hpscott.wordpress.com/