The problem is that the OpenJDK has problems with graphical toolkits, specifically Swing. Intellij (Java IDE with a lot of Swing) runs a lot worse under the OpenJDK than under the Sun's JVM. I might be wrong, but I don't think this has changed recently.
For a while, using OpenJDK was the only way to get proper font smoothing on Linux in IntelliJ. It doesn't display any warnings anymore and works fine with OpenJDK now.
I keep hearing this and I can't find any examples myself. I use IntelliJ occasionally and haven't had any issues using it with OpenJDK 7, though it does warn me IIRC. Similarly, with Minecraft, I've had no issues, though I'm not an avid player by any means.
Either way, it'd be a nice way to give Oracle the middle finger about this.
Because, I'll tell you what, I sure didn't get any crapware when I typed `sudo apt-get install openjdk-7-jdk`.