I've been doing an interesting experiment related to this. For the past month, I took either 200 mg Modafinil (Generic) or 150 mg Armodafinil (Nuvigil). I noticed no increase or decrease in my productivity. However, my mood was noticeably improved with both. I became more sociable than normal, which surprised some of my co-workers (usually I'm quite reserved / absorbed with coding during my day to day). I also was able to see certain novel patterns I wouldn't have before. It's hard to describe this: it's almost like my brain was bringing to the surface memories that were relevant to helping me solve a particular problem.