Consistency is totally killing GNU/Linux on the desktop for me. Ubuntu does a pretty good job at providing an usable desktop experience out of the box, and by that I mean decent UI, decent font rendering, decent defaults. However, it is not seldom that, for example, I have 4 windows open and each one of them has a different type of scrollbar. I know this is not important for many people, however, for myself this is totally killing it. I grab my Mac and I can focus on my work without being annoyed by the environment.
In the OSS world, many people feel no need to finish things and make them usable for the end-user. (I am looking at you, bcache.) Honestly I'm wondering why. Does nobody have the missionary drive anymore to bring Linux to the people, and everybody wants to just hack something to make it work for themselves? When do OSS developers feel rewarded and highly regarded -- when things work for them and the other people on their IRC channel, or when people start picking up the features they just wrote and actually using them?
Lack of system-wide spell check might be a contributing factor.