I've spent awhile perusing all the webboard discussions regarding cryonics, and decided to put my own opinions on the matter on the table.
It's actually ironic, since I intend on going on to earn my bachelor's in biochemistry and physics with the intent to study nanotechnology, and I couldn't be more against the practice of cryonics. My first turn-off to materials presented is their clear bias; the Cryonics Institute keeps informing me to "read more about cryonics for myself" and that it may be "the single best decision I make for myself." The material provides such nice, pat answers that sound perfectly reasonable -- they are all rather thin on second glance.
First of all, I don't believe that we'll have the technology ready to revive someone within fifty years, or even a hundred years. Examine your history. What were scientists predicting we'd have now a hundred years ago? What about fifty? What about ten years ago? In hindsight, it looks pretty silly. Fifty years from now, I'm certain present claims that we'll be reviving frozen corpses to life will look pretty silly as well.
Then comes the issue of money. Sure, a life-insurance policy would pay for post-mortem freezing. But who's going to pay for your re-education? Think about it. Assume you're revived a century from now. Considering the pace of technology, you'd be pretty out of the loop, probably for many of life's day-to-day activities, even. The Cryonics Institute doesn't even mention any sort of plan to reintegrate you with society, much less the expenses it would take to accomplish that.
Oh, and why would you even be revived in the first place? Not for historical reference, we keep decent enough records now. Were there enough of a downfall of civilization to lose our historical records, we certainly won't have the technology to revive anyone. With the population booming, we'll have enough warm bodies at hand, besides breakthroughs in robotics to perform menial labor. Sure, there should be a cryonics organization on hand to revive you, but are you sure they'll still be around? I wouldn't examine their perfectly reasonable answers, but examine your history for the past two centuries to answer that question.
Besides, when we finally establish this level of technology, it would be imminently useful for extending life spans, curing diseases, etc. Would we really use it to revive a bunch of outdated frozen people? Or on the currently living? Here's a better way to think about it: at that point, who's in a better position to decide?
My last point against cryonics is a moral one. In order to submit to freezing, you must both feel confident in your future society's good will to revive you, and not be interested in whatever religious afterlife you believe in, if any at all. So cryonics patients are people who have more faith in future man than in God; this is not the kind of moral fiber that I would wish to invite into my future society, because I have faith that my descendants would be more morally developed than myself.
To me, cryonics amounts to nothing more than a bad gamble.