I thought I'd do another update now it's been a while, in case anyone's interested in how Modafinil can work out long-term.
First: tolerance is a big issue. I know I used Modafinil a couple of times a few years ago, and that didn't result in any tolerance when I began this time round, but since taking it regularly(ish) over the last few months, I've not continued to achieve the effects I had when I first begun it again back in October, even after not having any for a couple of weeks. So tolerance may go away with breaks, but the breaks would apparently need to be very long ones.
However, it still produces noticeable effects with regular use. As I posted before, I experience none of the wakefulness it usually produces, but it does help my concentration - it's easier for me to get into certain activities, as I've already documented, and I can see why it's apparently popular with students.
With other activities though, I wouldn't even notice that I'd taken it, so it takes trial and error to work out how to use it effectively. I'd say don't use it if you want to be creative, and it also may cause difficulties if you want to switch from one activity to another. It doesn't help with energy for physical activities.
I was worried it would cause insomnia, but it hasn't for me, though that's almost certainly because I'm immune to its promotion of wakefulness, and everything I've read says I'm very unusual in this respect, not that I'm complaining - I hate not sleeping.
It didn't upset my digestive system, but it does somehow make me want to eat even less than than usual because if I'm focused on what I'm doing, I don't want to stop to eat; eating is definitely not one of the things it helps me to focus on. My weight is so low and I already have big problems with appetite, so this is a problem for me. But siince many people want to eat less, this could very well be a benefit for others. Modafinil has in fact been used as a weight loss med if I remember correctly. I don't know if it actually reduces appetite in some people or if they just focus on other things than food when they're taking it as seems to be the case with me. Anyway, I have to really force myself to eat when on it, which isn't good for me and probably wouldn't be good for quite a few others on this forum either.
I began it hoping it could help me reduce my codeine intake. I have significantly reduced my codeine intake since starting Modafinil, but I can't give Modafinil credit for it. It obviously doesn't help with codeine withdrawal, which I never expected it to, and since it also doesn't give me energy (which codeine does) it's no substitute for codeine in that respect. I also noticed, something I didn't really get from Modafinil at first but definitely have been lately, that Modafinil gives me anxiety (which is one of its known side effects). Anxiety interferes with concentration, so in order to benefit from the increased concentration Modafinil gives, I have to stop the anxiety. And codeine is so very calming. So basically Modafinil really works best for me when taken in combination with codeine. (I think I have to just face up to it: codeine is always good. I have reduced my intake, through what I guess you'd call will-power, but I'm not about to try and give up something so helpful. So long as my dose is reasonable and my doctor willing to prescribe it, I'm ok with it.)
So for me, Modafinil taken every now and then can help me get some otherwise boring tasks done and can help me really get info a state of flow and enjoy certain not-so-boring tasks. Despite the tolerance issue, I've found nothing addictive about it, physically or mentally (and as you probably guess from all I've said of codeine, I know what addiction feels like). I think I read some people can get physical withdrawal when stopping it, but I've certainly not noticed it at the doses I'm taking (200mg, maybe a couple of days a week, sometimes less regularly).
Usual disclaimer that I'm not a typical person and Modafinil affects different people in very different ways. The average person is likely to find it helps them feel a lot less sleepy and then suffer insomnia at night. It can also cause more digestive problems than I've experienced, which is probably something people on this forum should keep in mind.