About 3 or 4 years ago, I bought a roll of one hundred 37¢ stamps.  By 2006, I had not yet even opened the roll when they raised postal rates to 39¢, so I had to buy one hundred 2¢ stamps to make up the difference.  When they changed the rates again last year, I still had about 1/4 of the stamps remaining, so I had to buy a bunch more 2¢ stamps.

After having to affix 3 stamps to every letter I mailed for the past 7 or 8 months, I finally ran out of 37¢ stamps.

I think I'll stick to Forever stamps from now on.