Immortality in a sense of staying healthy at the same age forever while still being vulnerable to all unnatural types of death would be cool. And yeah, this medical technology might just be around the corner. Overpopulation wouldn't be a problem as long as people remember to use a F condom. It might just make the world a better place, who knows.
Any other kind of immortality is quite dangerous unless it's coupled with invulnerability. I mean, anybody here remember the Sloth from the movie Seven? Teleportation, time control, maybe a few offensive abilities too. On the other hand, If I were to ever find such a magic formula, there's no way I'd share it.
However, there is a combination of the two. I've dreamt about this since the movie Matrix.
Imagine being able to live forever inside a Matrix pod, always being aware that it's just a single-player simulation, always able to use any power, do anything you like and always able to wake up and hit the "kill" switch when you become bored after 200000 billion years.