On the "argument from boredom"
If you think that you might be bored if you are still alive 100 years from now, consider this: How bored would a person who was a young adult in the year 1907 be, if he were still alive (and young and healthy) today? He would have seen countless technological and cultural developments he could not possibly have imagined in 1907 -- antibiotics, jet airliners, movies, recorded music, space travel, the sexual revolution, the internet, and far more. Will the cascade of innovation stop for the next 100 years, leaving us in a world identical to today's except for our own extended life-spans? Of course not. It will not stop, it will continue to accelerate dramatically. You will not get bored.
If anything, my own expectation is that there will always be more interesting things going on than one person could possibly keep up with, no matter how long he lived. According to Ray Kurzweil's projections, by around 2045 we should have achieved the full Technological Singularity, with complete merging of human and machine intelligence, freeing humans from the limitations of biology (and from any limits on the increase of individual human intelligence, even to trillions of times its natural level), allowing us to lead lives so rich, deep, and free of external constraints over the individual as to be literally beyond the imagination of humans today. We in 2007 can no more foresee the cultural achievements and character of post-Singularity civilization than a bacterium could comprehend the pleasures offered by Shakespeare, the internet, or a simple lunch out with a friend. You will not get bored.
If you want a vision of a stupefyingly-boring eternity, consider the Christian view of Heaven. Since Heaven is supposed to be perfect, it couldn't progress or change. Most enjoyable activities, being considered "sinful" to some degree or at least hardly godly, would presumably be unavailable there. The traditional vision of Heaven would have me impatiently checking my watch after half an hour, never mind all eternity. Worst of all, the place would presumably be swarming with the kind of insufferable Bible-besotted prigs whose smug holiness makes everyone avoid them in real life, with the genuinely broad-minded, imaginative, skeptical, intelligent individuals having been deemed unfit for admission.
No thanks. I'm staying here -- hopefully forever.