Bookmarking Etiquette

Some notes on a brief discussion I had with Geoff yesterday about tagging behaviour, in particular: what’s the etiquette involved in shared bookmarking?
Geoff has previously written about social bookmarking as telltale and the advantages of brain subscriptions. He’d also recently pointed me at a New Scientist article discussing research which shows that email forwarding amounts to ritual gift exchange
Or rather, he bookmarked it in del.icio.us and I noticed it via my RSS reader and went away and read the article. I, like Geoff, subscribe to various peoples del.icio.us bookmark feeds as a way to find interesting and relevant content.
As we subscribe to each others feeds, the act of bookmarking has started to subsume the previous activity of email/link forwarding. I think this is another form of tagging behaviour thats distinct from both filing and annotative approaches.
The potential point of etiquette was this: if you tag something, as a result of a friend’s bookmarking activity, are you adding noise to their aggregator? After all, they’ve seen it already.
I think we concluded that it wasn’t. After all one might still legitimately want to bookmark something to file it away. This raised the issue of whether both public and private bookmarks are useful features. Furl has them I believe, but del.icio.us does not. There’s also the fact that the additional bookmark constitutes another hop through the social network graph.
As I write this it occurs to me that the feedback loop is useful in that it indicates that the “gift” was received and deemed useful or relevant. Certainly worth a bookmark. Annotation features provide a way to add simple comments that might also be of interest to the originator of the bookmark. A kind of tagging back channel?
Given the level of interest in this space, I presume that someone has begun classifying these different types of activity. The classification would include not only the act of tagging (is it filing, annotation, or sharing) but also the types of tags themselves which range from keywords through actions, such as toread, to the descriptive conventions I discussed here.