HFS+ case-sensitive or case-insensitive -- which type to use for the primary drive partition? What reasons are there for choosing the case-insensitive version of HFS+ when formatting the primary drive partition? Would case-sensitive not always be the best choice?
Use the default (case-insensitive) unless you both a) know what you're doing and b) you absolutely have to. There are several programs (Norton Antivirus comes to mind) that won't work properly on a case-sensitive file system.

HFS is, by default, case-insensitive but case-preserving (i.e. it doesn't care what you type for comparison purposes, but it will remember what you type).