It's not a "new" mistake, but reading these posts reminds me of the most common mistake made. People approach a new OS with the wrong attitude. Many people pick up Linux expecting a "free Windows." It's not Windows, it's a posix-compliant OS. Holding up OSX and Windows as benchmarks for GUI design is one thing, but expecting every OS to mimmick their every detail is utterly ridiculous.

Embrace diversity. Don't just pick it up and shake it. Read the documentation that came with the distro. Read the man pages. Explore the web for it's wealth of information on the subject. Then, once you're familiar with it, you can decide whether or not it's the OS for you. But experience it for what it is, not what you want it to be. If I need a red pen, I don't pick up a blue one and stare at it and shake it, expecting it to turn red.