I have NOT used it. If you are looking to become a conscientious lawn manager regarding environmental impact, it's always best to get a soil analysis done to have a base line of your soil nutrient levels and health, and then proceed from there. Not unlike caring for your body.
Milorganite would introduce an "organic" component to your lawn care that usually is a good thing.....microbes, organic matter, etc.. However, it contains NO potassium,a vital component for turf health. They don't address this on their site and you would want to apply supplemental K if your soil tested low. They also don't address pH....I would investigate that.
Phosphorous - many lawns don't require additional P (soil test) and even though the Milorganite P is more "stable" and less likely to leach, you could be adding a nutrient that is not needed AND could eventually leach.
While a regular fertilizer is applied at around 3 to 4 lbs./1000 sq. ft., the Milorganite is applied at 14 to 17 lbs. per 1000 sq. ft.. How does the cost work out?
Taking all this into account, I would consider it not as an organic cure all, but as "maybe" an alternative in conjunction with other lawn feeding programs. Lawnsite.com has an entire forum on organic lawn care if you wish to delve into that.
There's lots of opinions on lawn care. I personally think that the wide spread hyper chemical approach is wrong. But, I also believe that moderate, well thought out use of non-organic products is o.k. too. Some argue to feed the plant, while others argue to feed the soil. Balance and moderation is what I do. Returning the clippings to the lawn is excellent.