I've made the tradition down to lightweight trainers and heavier flats. I rotate a 9 oz lightweight trainer, an 8 ounce flat, and a 6 ounce flat for my normal running.
I was never particularly injury prone, but I had trouble with Achilles tendinitis coming and going in my old shoes, so I made the switch during a healthy patch, hoping to strengthen the Achilles and get rid of the problem. Results were mixed on that front, Achilles tendinitis still hits me over a year and a half later from time to time, but I ice, ibuprofen, and break out the 11 oz trainers for a few days until it goes away then resume normal training, so it never really interrupts my running. It is no more or less common than it was when I was running in normal trainers, but I've gotten a lot better at treating it and can usually get rid of it in a few days time.
My foot strike is noticeably improved. I never heel strike anymore, even at slow speeds, I used to heel strike down to around 6:20 pace, now even during recovery jogs as slow as 8:00 pace I midfoot strike, that is the biggest improvement I've seen.
Long story short, my injuries have not been effected positively or negatively for me, I might be slightly more efficient running now, but I didn't see any crazy improvement.
Overall, I'd say it is about a wash, I find I can generally squeeze more mileage out of lighter shoes though, so I've saved probably a couple hundred bucks by running in light weight shoes. That is the big selling point for me.