Back in June of 2011, I decide to try the Mizuno Wave Universe 3 flats (Model Number: 410375.0010). These are extremely light shoes, weighing in at a ridiculous 3.6 ounces. There is only a 2mm heel drop with a Stack Height: Heel (18mm), Forefoot (16mm).
I wore them in one triathlon and found they absolutely sucked for sockless wearing. The material has a fish net meshy quality to it. As result, I received seven blisters on the feet after wearing them. And I promptly forgot about them, taking them out only now and then for a quick pacing run. Wearing double socks, of course.
But I have found new use for them. That is as a treadmill shoe. On a treadmill, these are the bomb (do kids still say that?). They are a perfect show for those semi-intense to full-out-insanity treadmill efforts where a clunky 10 ounce shoe would just be a distraction.
The 3-series has gone the way of the Dodo, but you can get the 4-Series shoe, slightly heavier at 3.9 ounces but you won't even feel them on your feet. Slightly greater drop, coming in a 4mm rather than the 2mm found in the 3-Series. Running Warehouse lists it at $120. Road Runner lists it at $125, but if you are part of the VIP program the shoe can be yours for $112.46.
If you decide to try the shoe, I recommend to go up 1/2 size (US) from your current training.