Like CountingDown said, I learned that eating frequent, small meals is a very good idea!
I learned that I don't HAVE to always hate my body. Sure, there are things I am not fond of, and I am sure there always will be, but for the most part, I actually like the way I look.
I learned the importance of counting calories and that I can't personally lose weight on solely diet or exercise - it has to be both.
I learned that diets are bad, but lifestyle changes are good. Diet pills are generally uneffective, too.
I learned that I no longer have my teenage metabolism
I learned that alcohol has an INCREDIBLY IMMENSE amount of calories.
I learned the importance of protein in developing lean muscle.
I learned that I can look just as lean (and maybe even more so) at 135 as I did at 125. Like Susan, I learned the value of weight training!
I learned that not all healthy foods taste like butt!
I learned that eating healthy at restaurants is like finding a living fish in the desert.
I learned that exercise is actually really fun. For the longest time, I hated all physical activity. AND I learned that I actually like dancing now that I'm smaller - I hated it while fat because I thought I was too jiggly to try to look sexy AND I hated it while thin because no one taught me how to dance without looking like an idiot.