I have known quite a number of people who have taken modafinil, and none of them experienced more than minor side effects. I have several friends who stopped using it for long periods because they built a tolerance (tolerance != addiction), but none experienced withdrawal symptoms.
I used adrafinil for a while because it has the advantage of being unscheduled in the US, and I noticed weak tolerance building, but the only side effects I had were insomnia (while it was in effect) and mild headaches which went away with aspirin. The only reason I stopped taking it was that they revoked its approval in France, and none of the generics from other countries that I've found seem to work.
And you are basing this on what? When I went looking for studies, even the ones on patient populations like cocaine addicts, didn't report addiction: http://www.gwern.net/Modafinil#tolerance
... and what do you do when all of that's already taken care of?
I'm a bit of a consciousness-naut and self-experimenter who's obsessed about increasing productivity. I've experimented a lot with Nootropics.
My thoughts?
Modafinil. Stay away from it. The stuff is wickedly addictive and many people have experienced significant long-term side effects, especially if they try to go off it.
Piracetam. Does a lot to reduce ADD and has strong anti-anxiety properties. That said, I found the benefits (minimally increased focus and less anxiety) to be far outweighed by the fact that you have to keep taking the stuff obsessively lest you go into withdrawal (coming off the stuff is horrible once you've been on it for a couple weeks).
If you want to increase productivity and focus there are a ton of other things you can do, starting with the basics of exercise, proper nutrition, and meditation.