Thanks for the support.
A few notes on the difference between Pro and G3 (which I think we've communicated to gw280 unless I'm even worse than I thought I was at figuring out whose email address equates to which user name):
1. There is about a 120g difference in weight. However highly you value that weight savings is for you to decide. To me it's not a huge deal.
2. The electronics in the G3 are more easily serviced. You open up the cap, you pull the brains out, you send the brains in for service. With a Pro, you have to send the whole wheel in if it needs service. When Cycleops was closing out the old Pro+ and SL+ models about 18 months ago (someone above mentioned getting one from that time), there was a higher than normal incidence of an incorrectly/inadequately soldered battery clip. Apart from that, our experience with Powertaps has been that they're pretty remarkably reliable. I have owned at least one since 2008. The first one I owned was bought second hand and was from the era when they weren't exceptionally watertight. Eventually water killed it, and I was able to upgrade it for a pretty reasonable cost, even though I was not the original owner and they knew that. Since then, both my wife and I have used them with not a day out of service for either of us. Since about 6 weeks ago I use a Quarq, but that it 100% because I need to have the flexibility to use whichever wheel set I might be testing without it screwing up my training (I am a princess about training with power and will throw tantrums if I can't). My Powertap is now on my cx bike, on which it gets flogged hard to no ill effect.
3. The, to me, bigger benefit of the G3 hub is the geometry. (caution wheel geek content ahead) On the Pro, the right hand flange is 15.9mm off center and the left is 33.9 off center, and both flanges are 70mm diameter. These flanges are far closer together than you'd ideally want, but it gets necessary because the electronics need a big diameter hub tube to fit inside of, and the left end cap on the Pro is a space hog. With the left flange being as high diameter as it is, it needs to be well inboard in order to get any tension whatsoever on the non-drives. Because the G3 uses a smaller electronics setup, they can use better geometry. The geometry on the G3 is in fact pretty similar to that found on some of my favorite hubs.
If you are using a carbon or aluminum rim that can take high spoke tension (125kgf or so), and have 24 spokes or more, then the Pro will make a fine build. Most aluminum rims, I'd really recommend 28 rear unless you are very light. I'm 165 and not exactly Andre Greipel in the top wattage category and use 28 spokes on my aluminum rear wheels, and that's with hubs that have better geometry than Powertap Pros. The Pro is intolerant of sloppy builds, so the build has to be good for it to work or else you will be coming out of true all the time and eventually breaking non-drive spokes. If you are using a rim that is intolerant of high spoke tension or has 20 spokes, go G3. Also, if you are say 180 or above or very powerful (I am neither), I recommend G3.