Ultimately, it depends on the architecture that your machine has.
(background) Nodes can solely store data in their properties. Their properties are stored using a key-value store. (per here)
The value in each property is limited to Java primitives (ints, floats, etc.), strings, and arrays of primitives/strings.
Therefore, the maximum amount of data a particular property can hold would be limited to the maximum size for a string or the maximum size for an array of strings (that's per node). This limit (for 32-bit machines) is 4GB. (Note that this may be limited to 2-3 GB.)
(Also, having said this, there was a bug previously that limited string size to 1 MB. I expect that this is resolved.)
Of course, this raises the question of whether multiple properties could store more than 4GB per node. Since the properties list is essentially a key-value store, it would expect that the maximum size would be limited by disk space and key selection. I can't find anything to support or deny this, however.
That doesn't definitively answer your question, but from what I understand you should be able to store large amounts of data per node (up to disk space capacity).