By setting a certain bash environment variable, you can limit which commands are kept in the .bash_history file. The following options can be passed to the HISTCONTROL environmental variable:
ignorespace - omits commands beginning with a space
ignoredups - omits commands that match the previously run command
ignoreboth - combines ignorespace and ignoredups
erasedups - removes previous lines that match the line that was just run
To set it, simply run the following from the command line, or add it to the .bashrc or a single user's .bash_profile:
export HISTCONTROL=ignorespace
If no value is set, then all commands will be saved regardless of their content.
even better:
export HISTFILE=/dev/null
Nothing says "propritary one-liners" like writing history to /dev/null!