Dan Connolly blogged about units in RDF.
We have the same problem in Nepomuk, but for more practical things like measuring the size of a file (MB, KB, B, b) or the length of a song (1h, 3m 20s, 200s). Actually, we are searching for a solution that will work in normal KDE and doesnt require a PhD to understand, the typical KDE developer will take 10 minutes reading the FAQ and then start using it (note: 10 minutes for RDF, Turtle and the Unit ontology đ
Will blog again once I have checked what our status is.