Sure!

Some positive ones:

1) Spot-on prediction:

  PROMPT: lines with 3 or more characters or lower-case letters

  PRED: ((.)|([a-z])){3,}

  GOLD: ((.)|([a-z])){3,}

2) Learned to generalize and produced a simpler regex:

  PROMPT: lines with a character and the string 'dog'

  PRED: .*(.)&(dog).*

  GOLD: .*((.)+)&(dog).*

3) Also learned to generalize and produced simpler regex without duplicate logic:

  PROMPT: lines not containing a letter

  PRED: .*~(([A-z])+).*

  GOLD: (.*)(.*~([A-z]).*)

4) Handling multiple references correctly:

  PROMPT: lines using 'su' after 'sun' or 'soon'.

  PRED: .*(sun|soon).*su.*

  GOLD: .*(sun|soon).*su.*

Though I find the mistakes interesting as well!

1) Issues counting properly:

  PROMPT: lines containing a 5 letter word beginning with 't'

  PRED: .*\bt[A-z]{5}\b.*

  GOLD: .*\bt[A-z]{4}\b.*

2) Misallocation of parenthesis (to be fair, the prompt is slightly ambiguous):

  PROMPT: lines with 'dog' follwed by 'truck' and a lower-case

  PRED: (dog).*((truck)&([a-z])).*

  GOLD: (dog.*truck.*)&(.*[a-z].*)

Mistake 1 - Looks like the classic off-by-one! Definitely the boundary point for a Chomsky Grammar type. Modifications to the code for processing problems like the Sorites paradox would be interesting.