my favorite prediction about the future was written in 1899.  the writer predicted that by 1999, at the then-current growth rate of the horse population on manhattan, the entire island wood be buried in horse poop! 

the following quotes are more 20/20 hindsight...

"Louis Pasteur's theory of germs is ridiculous fiction".

- Pierre Pachet, Professor of Physiology at
Toulouse, 1872

"The abdomen, the chest, and the brain will forever
be shut from the intrusion of the wise and humane surgeon".

- Sir John Eric Ericksen, British surgeon, appointed Surgeon-Extraordinary to Queen Victoria 1873.

"Professor Goddard does not know the relation
between action and reaction and the need to have
something better than a vacuum against which to react.  He seems to lack the basic knowledge ladled out daily in high schools."

- 1921 New York Times editorial about Robert Goddard's revolutionary rocket work.

"If I had thought about it, I wouldn't have done the
experiment. The literature was full of examples that
said you can't do this."

- Spencer Silver on the work that led to the unique
adhesives for 3-M "Post-It" Notepads.