Many have already commented on the fact that intelligence can mean a decline in happiness. I would say it is true, as ignorance truly is bliss. The smarter you are, the less you can relate to those around you, and thus, those you consider peers or friends will decline... (Well, with the exception of all those ANGST filled people out there). I remember House having an episode being a good example of this.
Heres an interesting thought- There is one theory, that each individual will never experience their own death, so technically, trading those years of your life will have no real impact.