Agreed! I just started using a pair of 600EX-RT with the ST-E3 with umbrellas and stands on my 1D-X and I am very impressed. Previously I was using a pair of 580EX II for indoor shoots and a pair of 430EX II with PW TT5's for outdoor shoots (because of the RF interference of the 580's).
The 600EX wireless is worlds above the Flex units and much easier to operate and quicker to setup. The only downside is the 100ft limitation vs. ~1200ft for the Flex (I assume with 430's as my 580's would never work more than 6-feet away). But that certainly isn't a problem for me as around 25-50 ft is my max distance.
My biggest gripe with the PW Flex units is the slow adoption of new bodies. I've had my 1D-X since July and I still cannot use my TT5's because they haven't come out with a new firmware. It was the same with my 5DMkII when it first came out. No more calibration shots, no more hypersync calibration, no more missed triggers, no more hidden settings and no more USB / laptop. I am so done with the Flex units.
I've already sold all my 580's and 430's and the TT5's are currently on the block.
I'm still keeping my original set of PW Plus II's for multi-vendor compatibility with studio strobes when I run totally manual. They are about as fool proof as it gets but I must say the new 600EX-RT / ST-E3 is a close second!