Following up on the disambiguation thing, once the aggregator knows that it's dealing with multiple senses of the same tag, the strategies become much more obvious. Here's a couple of ideas:

Indicating other similar usages

Am thinking that a graph could 'import tag-senses' from another graph. I.e. effectively saying 'if you're trying to 2nd-guess what I'm talking about, I probably mean the same as things in this document'. Something like: http://my/document/ similarVocabTo http://some/other/document/

This strategy could be used to e.g. import well-defined tag based ontologies and vocabularies.

Statistical Analysis

Once you have enough data, another potentual tool for disambiguation is statistical analysis (once you know there is ambiguity). E.g. you could use statistics to guess the cardinality of a property (to a certain level of error). Something like : 'eyecolour is something that practically all resources only appear to have one of. Therefore the PhilDawes with brown eyes is likely to be different to the PhilDawes with blue eyes.'