I disagree that PurpleNumbers are granular since PermanentAnchors can index each word in the text. I prefer a PermanentAnchor over a PurpleNumber especially in a wiki context. It has the advantage of being based on words instead of numbers, which means it is immune to reordering of paragraphs. The idea of the link is to track an idea, not an addressable byte, so I feel this works better. Of course that doesn't mean it would work for a WebLog since arbitrary commentators cannot annotate your blog with links. Essentially, the issue there is that since you cannot negotatiate a "smallest set" of annotated links, you flood the text with every possible link. Therefore you must resort to numbers instead of words.
Sunir, the level of granularity has little bearing as regards the basic issues of addressability over changes made during a document lifecycle. The idea of purple numbers is that a paragraph represents a closer approximation to an "idea" than does a word, that words aren't necessarily in and of themselves even significant. In practice, there doesn't seem to be (to me at least) any need for granularity at the word level. Furthermore, the current technical approach to linking on the Web suggests word-level links would be enormously impractical, whereas the idea of adding a link to a paragraph doesn't alter the landscape much, it's just a few added links in an HTML document. Link management in purple number systems is albeit a bit primitive, but works okay. This would benefit from integration with a version control system that handled the two kinds of links (the structural ones that change when the document changes, and the "canonical" ones that don't). But between word- and paragraph-level addressing, they are both granular, it's just a matter of level.
One thing that also occurs to me is that purple numbers are meant predominantly as link targets, not outbound links. Their purpose is therefore a bit different, as a means of permitting other people to create links to a specific portion of a document, generally at a level of granularity that is deemed practical.
My criticism is only that on a wiki one can write a link target in anywhere one wants, whereas on a weblog the annotater cannot. Thus, on a WebLog or any static page PurpleNumbers work well for the the simple reason that these webpages can only be edited by TheAuthor and the author cannot predict in advance what an unknown annotator will comment on. Therefore he must create a addressable target for every paragraph, whether each is particularly meaningful on their own, rather than limiting the targets to the flow of annotable ideas. So, links to every paragraph are overkill. In my mind, I am thinking of PermanentAnchors as headings, which are rhetoric related to print. PermanentAnchors are a rhetoric related to wikis, I'm positing. -- SunirShah
An alternative idea is to link each word in blog posts: [Pink Numbers]... but I think diveintomarks' point is that the hash signs placed in the text of PurpleNumbers? become distracting. But don't you think pink bears are more cute?