While I've never used Modafinil, I have used Adrafinil often in the past when dealing with insomnia and having to work. Adrafinil converts into Modafinil, and you don't need a prescription in the states. It worked quite well for it intended purpose, which was to make me not feel so sleep deprived at work. I don't really remember it having much effect on my mental state, but maybe I just never noticed and I have no clue what it would do if I used it after getting enough sleep. I figured if I took adrafinil without being sleep deprived, I wouldn't feel it. Kind of like an OTC painkiller, in that if you're not in pain, you won't feel any different after taking it.
I couldn't use it for more than two days a week though, because on the third day, it would do nothing. Even the second day, it wasn't as effective. So I always saved it for the day I was the most sleep deprived each week. I'm pretty sure I have a few left. If I do, I'll take it again just to see what it's like now that getting more than 0-4 hours of sleep for five days out of the week for five years. I do have serious fatigue from depression so maybe a weekly boost isn't such a bad idea. We'll see.