The following are errors I have found in HOWTOs that should be corrected:
Linux IPCHAINS-HOWTO
Section 4.1.4.6 says that to handle packet fragments you can set a kernel option when compiling. This is no longer true (as of 2.2.13 I think). The correct method to enabel defragmentation of packets is:
echo 1 > /proc/sys/net/ipv4/ip_always_defrag
NFS HOWTO
Section 3.4 states that NFS exports are read only (ro) by default. This is incorrect for many Linux NFS systems which mount read/write (rw) by default. Check your local documentation to be sure (or just specify read-only in /etc/exports to be sure).
If you have other errata, please let me know.