The Linux 3.0 kernel would have been released as the Linux 2.6.40 kernel, until the developers decided to end the 2.6 series and move forward with the 3.x series.
This Phoronix posting details some of the Linux 3.0 features, including file-system Cleancache support, initial Intel Ivy Bridge support, better open-source kernel graphics drivers, and many other hardware driver enhancements.
"So there it is. Gone are the 2.6.
Now it's time to start getting excited about the Linux 3.1 kernel. With the initial 3.1 kernel plans that were talked about yesterday, the merge window may be slightly off (longer or shorter) due to Linus Torvalds taking a holiday next week.