Apple unleashed OS X 10.11 El Capitan just under two weeks ago, and if you've not already pulled the trigger on the upgrade then I suggest you put your upgrade plans on hold until the first update is out unless you like dealing with bugs.
Every new operating system has its bugs, but El Capitan seems to have more than its fair share of show-stopping bugs, so much so that I've resisted installing it yet on any of my mission-critical systems (and regular readers will know that I'm not known for being cautious).
Apple's support forum is awash with bug reports, ranging from annoyances such as applications not working and external drives not mounting properly to devastating bugs involving unbootable systems and lost data.
While the Apple faithful want users to focus on the benefits of upgrading to El Capitan, what I'm seeing is the rockiest, most buggy OS X release I can ever remember, and the first time since OS X has been available for download that I've not upgraded all my systems on day one. Having dabbled with both the betas and final release on test systems, I've touched on enough issues to make me uncharacteristically restrained when it comes to 10.11.
There's a good chance that I could be lucky and dodge (or at least work around) any issues I encounter, but quite honestly I can't find anything new in El Capitan that's worth potentially wreaking a working system over.
It seems that the extensive public beta didn't really help when it came to delivering a polished product, and it affirms my belief that public betas (and not just Apple public beta programs) are more of a marketing tool used to generate hype rather than a way of shaking out bugs.
My advice is that if you're not already upgraded to El Capitan then wait for the OS X 10.11.1 update to be released, which squashes many of the bugs that plague the initial release.