Update...
I like the Williams wheels. After riding my Bontrager Race XXX carbons and the System 30s, I would rate the 30s slightly stiffer ride but more lateral stiffness than the XXX lites. The 30s are more stable descending. I am not ready to say the 30s are faster than my other wheels since I have not done any quantitative testing.
I rode the 30s in some very strong cross winds last night. They were not a problem but I did have to lean the bike into the wind but not more than I have had to do with other wheelsets.
Braking on the System 30s is good but not as good as aluminum. The 30s use niobium rim material that allows for the deeper rim with lighter weight. The niobium is soft and using the standard brake pads metal shards embed in the pads and make scratching sounds when applied against the rims. Williams said, this will go away with time. However, I believe that the best solution and Williams agrees is to use the Swiss Stop pads. I will give them a try this weekend.
The power meter is totally cool but not without its trials and tribulations. As an electrical engineer / finance guy, I do not mind playing around with "issues". When I got the power hub, it quit measuring power after 3 rides. I sent the wheels back to Saris and they replaced the hub (very good customer service). The new hub worked fine and then the speed was off by a factor of 2 - two times faster. Saris was clueless but would do anything I wanted. I called Garmin and after a one hour discussion with customer service and level 3 tech support from engineering, we think we have the problem fixed. The hub works fine, the 705 works fine and I am happy with the result. I think Garmin will need to revise their latest firmware in the 705.
Notwithstanding all that, the Garmin 705 with the PowerTap SL+ is a very slick high value solution once coupled with Training Peaks software. I can use the wheel on my road and TT bikes easily.
I purchased the book by Allen / Coggan "Training and Racing with Power Meter" and it is very interesting and provides IMHO, very good insight into cycling performance and how to use the power meter to get the most from it.
The information collected by the Garmin / PowerTap combination once loaded into Training Peaks offers a compelling presentation of my performance, strengths and weaknesses. I really like this information a lot and it dwarfs other software / performance data that I had been using.