Windows Vista
Switching to Vista would require that I buy new hardware (for several computers), and the operating system itself is pretty pricey. The cost of moving to Vista far outweighs the benefit for me.
For a new computer, I could switch to Vista, but I can also buy a Mac. With a Mac I expect a better user experience, and the fact that MacOS X is Unix underneath appeals to me on a geeky level.
For my existing computers, I can continue running Windows XP for now, but I need to plan on Microsoft discontinuing support for XP at some point.
I’m reconsidering Linux as a primary desktop operating system.
Since I tend to read words on my computers, I care about how clear they are. I recently compared Windows ClearType font rendering with subpixel anti-aliasing on Linux. Below is an image with the two side-by-side (Windows on the left, Linux on the right) — click it to see what I had to say about it.
(Note that ClearType and subpixel font rendering may actually look worse than traditional anti-aliasing on a CRT monitor. They’re intended primarily for LCDs.)