Why do I see a 'Yay' with a 70% match, and a 'Booo' with a 75% match?
I think that it shows "booooo" when a share is rejected, and "yay!!!" when a share is accepted.

In x/y (z%)


x is the number of accepted shares
y is the number of total shares submitted (accepted+rejected)
z is x/y as a percentage (the percent that are accepted)



  Why do I see a 'Yay' with a 70% match, and a 'Booo' with a 75% match?


Because you had a success which raised you to a 70% success rate, and later (after a few more successes) had a rejection which lowered you to a 75% success rate.

(BTW, I hope you know that mining any SHA256 or Scrypt coin on a CPU is almost certain to cost you more than it can earn you)