Passed Linux+ today with 750. I have about 3 years experience working with BSD/Linux and studied for about a month; and this exam isn't as easy as it may seem. There was only a few IRQ/hardware type questions. But basically the things to know:
iptables
route
tripwire
samba (mounting/configuration)
bash variables
basic shell scripting (if,while,end,done,fi)
scheduling (at,cron)
encryption (SHA5,MD5,DES,etc.)
USB
SSH
NIS!
printing
networking w/ troubleshooting
I studied mostly with Testout Linux+ (got for free :P) and a little with Linux Bible. But the most helpful was probably
http://www.mcmcse.com/forums/exams/. The pretests are very similar to what kind of questions to expect.