I took the CompTIA Linux+ test around 3 years ago, and all I used was experience, and the Sybex Linux+ study guide.
I can tell you that you will need to know a lot about Red Hat, Debian, and general package manipulation. The test spends more time on RPM than any other package management, know your basic utilities (vi, sed, awk, grep, etc...) and learn about RPMs.
It wasn't that hard, but it wasn't as easy as I figured it would be. The questions may be a little outdated, but they still apply to any current distro.
I can suggest the Sybex Linux+ study guide, and you will probably want something else, because without the years of experience I have had on linux, I would have failed, because the book covers only about 1/2 of what you need to know.
Most people will tell you it isn't worth it also, but it has opened a few doors for me, and at the very least, gets your foot in the door and looks good on a resume.
http://www.amazon.com/Linux-Study-Gu...2802253&sr=8-1
I am pretty sure that is the book I have, I will have to check. I am at work right now so I can't.
If you need to know anything else, just ask. I will be happy to help in any way I can.