Pros: it's killer for jet lag -- I fly between the US and HK fairly regularly, and suffer extraordinarily from jet lag. Modafinil helps a lot in reseting my internal clock. I also see the deep concentration effect, particularly on a project that I'm avoiding due to the inherent dullitude -- when high, I can power through stuff that I would deflect and ignore.
On the down side, if I forget and drink a beer after taking Modafinil, the hangover is epic. Too, it makes my pee smell really weird. And I have a tendency towards chatterboxery, which is exacerbated beyond all reason.
As people point out above, this is a good thing. Makes counterfeiting that much harder. It would be nice if all drugs came with such signatures of authenticity. ('Remember, real Viagra will cause a little shamrock tattoo to appear under your right armpit for an hour.')
On the down side, if I forget and drink a beer after taking Modafinil, the hangover is epic. Too, it makes my pee smell really weird. And I have a tendency towards chatterboxery, which is exacerbated beyond all reason.
Anecdotes/evidence/&c.