A cent is a factor of 2^(1/1200). There are 1200 cents in an octave, which is a doubling in frequency: if we have 1200 of them, 2^(1200/1200) = 2^1 = 2.

Lisp-wise:

  2> (exp2 (/ 1200))   ;; exp2 is courtesy of ISO C 99
  1.00057778950655

So, it is a .0578 percent change in pitch, or determiner of pitch like record rotations speed.

There are 100 cents to a semitone - by definition. The frequency shift of a 25 to 40 cent adjustment isn't likely going to be noticed by the average listener. A lot of times you don't notice it until you try to play guitar along with the song and you notice something is a little "off."

In can drive you nuts when you're playing by ear because when trying to find the root note, i.e. the key, you'll find it between two semitones. Always go for the lower tone. For example, if it sounds like it's a little sharper than A, but it's definitely not Bb, then you know it was A and the mastering was sped up. That's another thing, in my experience it's always sped up and never slowed down.

I have a theory that one of the reasons Eb standard guitar tuning started becoming so popular in the late 60s and into the 70s was because the speed up was getting to be so common that guitar players started adjusting their tuning for it, not to mention you generally get a "heavier" sound.