Mavericks, regardless of it's improvements or changes, does one thing that affects FCPX in a negative way. Thankfully it's easily fixable. The new system feature, "App Nap", which reduces unneeded drains on system resources by background applications (think Flash player) has the unfortunate side effect of stopping background exports in FCPX if you switch to another program. This is fixable by highlighting FCPX in the Application folder and selecting Get Info. In the info window you will find a check box that prevents App Nap for FCPX. Enable that and you are back to background exporting. All applications have this option now.

Awesome thanks!

I also like to say Thank You.
Why cant we be informed by Apple of these things?. How many other little gems are hidden regards FCP-X?

Not sure this is "hidden" so much as it's a natural progression of balancing user needs.

For someone NOT doing video editing or other mission critical creative work, longer battery life for your laptop is a great goal. And App Nap supports that.

For those of us who do edit - a way to defeat that useful improvement is also required - and Apple has provided exactly that.

I'm not sure I'd make a huge deal out of a function that will only affect a relatively small subset of the universe of all Mac Users.

My 2 cents, anyway.