With all of the recent buzz about the Minecraft End User License Agreement (EULA) it is no surprise that when running a server you will now need to agree to the terms outlined by Mojang. You can read more about the current rules for monetizing a minecraft server in this post. Many have become nervous that this will make it impossible for them to make money off of their server, but that is not the case. There are still plenty of options available to monetize your server.
One significant change that was made in the latest update from Mojang in Minecraft 1.7.10 is the necessity to agree to the EULA in a file placed on the server. You will not be able to start a server unless this eula.txt file exists and you have set eula=true inside the file. It comes by default as eula=false and new servers will not even start until this is changed. You can find out how to change the eula.txt setting in this knowledgebase post. After you have read through and accepted the changes you will be able to start up your server. Just keep in mind that by doing this you must not break the rules defined by Mojang in regards to how you are allowed to generate revenue from a Minecraft server.