I've been using Linux for a long time, and I learned to use it by installing it and using it as my primary operating system — as far as I'm concerned, the year of the Linux desktop was in 1994 or so. Since then I've actually bounced around to a variety of operating systems and even single-booted my primary machine into Windows XP by choice, using Cygwin as a crutch. I've been running Linux solidly since Ubuntu Dapper, using Windows only on inferior (and seldom-activated) computers or in virtual machines to close corner cases like my mobile phone. Throughout that time, I have basically never been satisfied with the default appearance of the system.
This is a pretty simple one: Printing on Linux sucks. Adobe knows more about printing than anybody. Printing PDFs on Linux with Adobe Reader is wonderful. Conclusion: See title. For further discussion, see below.
Today, I tried to buy some DVD+R DL media from Newegg. It's not like it's a major sale, but it was lost because I couldn't use their site. I enabled javascript for newegg.com, but there was no shopping cart button, and when I backed up to the shopping cart page, the cart didn't work. Even the FAQ is Javascript-based and doesn't work here; I was unable to read the FAQ. Because they're on the west coast, I'd have to wait two hours to place a phone order, and I don't want to wait.