Categorizing with spaces
Jon Udell's been paying a lot of attention recently to categorizing XHTML elements. Two of his readers suggested that he use the class attribute, delimiting the categories (if necessary) with spaces; this is also valid CSS. I'm in favor of it as well, as it has worked well for me in two other circumstances.
At del.icio.us/crysflame, I keep a notebook of interesting links. Each link has several pieces of metadata; of interest is the tags field. The content of this field is a space-delimited list of categories, so to speak; a blog post about Google's IPO would be assigned "blog business", while a paper about graphing social dynamics would get "science social math". It's worked out very well for me, so far; I can find things easily enough by selecting individual tags, though more complex slices of the data aren't provided.
With the release of iTunes 4.2, a new field was added: grouping. At first, it was thought of as a similar sort of categorization field as the tags field: a space-delimited list of single-word categories. It turns out, however, that Apple has other plans for this field. While this puts somewhat of a damper on efforts to sort through music easily, the comments field can be used instead.