People who admin message boards (and I admin 103 boards) NEED to be able to view the posts in FLAT mode and NEED to be able to see 50 messages per page (newest first) inline/flat view. It is the ONLY way to properly and thoroughly review lengthy threads. For that reason alone I strongly feel that the default should be changed to: FLAT view, Newest first, 50 messages per page.
Back when the default was originally set to 10 messages per page in 2001 many users were on dialup but that isn't the case these days. 50 messages per page makes much more sense. Of course, if the cookies worked to correctly set out choices it wouldn't matter but as things stand now many admins cannot properly review lengthy threads.