Case 1: George Harrison and The Chiffons
To me the structural and melodic elements of these two ditties is fairly similar, however they are not similar enough to be considered a direct copy. There are only 12 different notes you can use in western equal temperament, and all of the melodic and chordal combinations possible have already been done. This combined with the fact that they lyrics are completely different brings me to the conclusion that Harrison should be found not guilty.
Case 2:Terry Gillam and The Chair
This, to me, is blatant art theft. Just because Terry Gilliam took the drawing and recreated it in another medium doesn't make it a different work. Terry Gilliam obviously knew he was copying "Neomechanical Tower (Upper) Chamber" because he admitted that he'd reviewed a copy of the book containing the artwork. Therefore, I find him guilty.
Case 3:Kier Smith's Oh So Criminal
Oh So Criminal was intended as a response to the Australian Government's "Fair Use and Other Copyright Exceptions: An examination of fair use, fair dealing and other exceptions in the Digital Age" Issues Paper, provided in May 2005. It used popular culture and well known icons in a 'mashup' which blatantly and intentionally breached copyright. It's creator, Kier Smith, believes that some copyright infringements should be let go as "fair use" and that the laws currently in place need many exceptions before they can be considered fair.
Kier's work is undoubtedly a breach of copyright, however it would seem silly to charge since it is the entire point of his work.