Autodesk supports a developer registration scheme to prevent node conflicts between different applications. Each registered developer registers with Autodesk one or more "Maya Node ID Block" to use in any Maya custom node saved into a Maya file. Of course, a developer may not choose to use an ID already registered by another developer.
Autodesk policies governing Maya Node ID registration. Autodesk reserves the right to:
Autodesk will take reasonable steps to register ID Blocks on a first come, first served basis.
Questions about registration and why you should register are answered here:
Why register a Maya Node ID?
To ensure that each application is installed in a unique environment, a unique registered developer Id for a Maya Node should be obtained by each application developer. In Maya, both intrinsic and user-defined Maya Objects are registered and recognized by their type identifier or type id. The basis of the type id system is a tag which is used at run-time to determine how to create and destroy Maya Objects, and how they are to be input/output from/to files. It is very important to note that these ids are written into the Maya binary file format. So, once an id is assigned to a node or data type it can never be changed while any existing Maya file contains an instance of that node or data type. If a change is made, such files will become unreadable.
How many IDs do I need?
For plug-ins that will forever be internal to your site use the numeric range 0 - 0x7ffff (524288 ids) which has been reserved for such plug-ins. In any other case, you need to reserve your own range which can contain up to 64, 128, 256, or 512 unique IDs.
Am I restricted to a small range?
No, you can reserve as many blocks as you want at any time. Consider registering only what you need. 1 for each individual node.