Thomas Mallon writes a biographic article about Harper Lee in The New Yorker. The article points out, as any article about Lee should, the fact that she never wrote a second novel after To Kill a Mockingbird. This fact lends some support to speculation that a large part of the book was written by Lee's friend Truman Capote – a theory disputed by the "extensive editorial correspondence" between Lee and her publishers. Describing the beginnings of the collaboration, Mallon writes:
He put her into his fiction at least twice—as Idabel Tompkins (“I want so much to be a boy”), in “Other Voices, Other Rooms,” and as Ann (Jumbo) Finchburg, in “The Thanksgiving Visitor.” Lee did the same for him in “To Kill a Mockingbird,” turning the boy Truman into Dill, an effeminate schemer with an enormous capacity for lying. One year, Lee’s father gave her and Truman a twenty-pound Underwood typewriter, which the two children managed to shift back and forth between their houses and use in the composition of collaborative fictions about the neighbors.
On to other matters: Mallon seems to have liked the 1962 film version of To Kill a Mockingbird more than the book, finding it tighter and less cloying. Notwithstanding some of my previous reservations about the film, his reasons are hard to deny.
Mirkwood 
Collin,
My opinion on whether Lee wrote Mockingbird, is a rather dry "I don't know for sure". Until I read Truman Capote's work, and get an idea about his style, I can't even make an educated guess. At this point, I have to just get by with "believing" that Lee was the person who wrote the book, and that the Capote connection is just a conspiracy theory.
Thanks again for your suggestions in the main review. With practice, I think my posts will start becoming more accessible.
P.