I design things that need to be really well sealed for a living. The powertap is a pretty "marginal" design....more like "spash resistant" than waterproof. I put some heavy marine grease over all the likely entry points and that seems to help.
To the Powerap tech: If the designers at Powertap would just read the "Parker O-ring and Seal design handbook"....it really works.
Our only model currently available is the G3, and it has a completely different design. It's sealed much differently than the old stuff.
I had my fair share of Power Tap issues [SL+] and the service dept. was top notch. Mine was with bearings. We had our discussions about them and they insisted their design was top notch. Needless to say, bearings should last longer than a couple hundred miles. They eventually replaced the entire hub. I have had little issues since then.
My biggest issue was the cost of getting the wheel to them for service and because of that, I would think twice about purchasing another Powertap product. I probably spent enough money to purchase two Powertaps with all the additional expenses I ran into for shipping and wheel building.
Yes, we have had issues with the bearings in the past. A couple hundred miles is not typical for our old bearings though. Currently we spec Enduro's Stainless Steel bearings rated at Abec 5 and they are indeed much, much better than the old ones.
As for the shipping, it really shouldn't cost that much. I've seen some people go overboard with the insurance on the wheels (not saying you did), but typically when I've shipped wheels on my own accord it hasn't broken the bank. Also, just for reference, we don't require disassembling the wheel for service either. Sending the whole wheel is completely fine.