I had no response to Modafinil at all. I started at 100 mg and worked up to 400 mg (under my psychiatrist's supervision), but at 400 mg, both he and I decided it wasn't doing anything — positive or negative — so I quit taking it.
After researching the subject a bit, my guess as to why Modafinil had no effect on me is that I probably have the wrong variant of the rs4680 gene. rs4680 is known as the worrier/warrior gene; those with the AA variant tend to be neurotic, have high anxiety, and handle stress poorly (my personality in a nutshell). Studies have shown that people with this variant of rs4680 do not significantly respond to Modafinil, so I suspect that I am one of them. I plan on sending a DNA sample to 23andme soon to confirm whether or not my hunch is correct.
With regard to getting a prescription, I'll note that my psychiatrist couldn't prescribe Modafinil directly to treat anxiety, so he indirectly prescribed it to address the "sleep issues" that were caused by my anxiety/depression.
For me, 5 mg of Adderall does what I was hoping Modafinil would do. Personally speaking, productivity is far more important to me than "feeling good", which is what I think a lot of people abuse Adderall for (and it certainly does produce that "feel good" sensation at high enough dosages). But at 10 mg and less, it's like a much "smoother" version of caffeine. In fact, lately I've found that I don't really like caffeine anymore because it makes me crankier, sweatier, and more jittery than Adderall does, and it doesn't help my ability to focus as well.