As much as this sounds like blasphemy to the open source community, I don't like Linux as a desktop operating system. Now don't get me wrong - I love Linux as an operating system. It makes a really awesome server. Unfortunately, even though I've written many applications for X, I do not like X. I don't like it the same way my friends at Apple Computer Corporation 9 years ago didn't like Windows 95.
I remember a discussion I had with my buddy Scott Boyd back in 1996 about Windows 95. He said "It's the lack of a hardware cursor that just feels wrong." I argued that it really shouldn't make a difference. 9 years later, I know he was right.
It's the nit-pick things that bother me about X. It just doesn't feel "crisp." It always feels like I'm running in an emulator, and because of the way X works, it's really what I'm doing.
I've been silently waiting for a "good" replacement to usurp X as the desktop GUI of choice for a long time now. Unfortunately, trying to replace X with just about anything else these days is going to be very difficult. The momentum of the graphical operating environments that ride on top of X (KDE, GNOME to name a couple) is enormous, and having to either rewrite a lot of the code or figuring out how to build a compatibility layer would be a huge undertaking.
In the past 3 years, it's gotten better, but there's really only so much a developer writing software on top of of the libXt, libXm, or even libX can do. They're still at the mercy of how X performs, and it just doesn't feel right to me.