Deepak and Neil blogged today about tagging and adding more structured metadata to the science web. I started by commenting to Deepak's post but it grew a bit so I changed it to a blog post.
The most obvious start for me would be to find a standard to communicate information on the perceived impact of a paper (extending hReview for example). It has a unique digital identifier and ways to resolve it but no way to communicate number of downloads at publisher site X, number of incoming citations in other papers, in blog posts, simple rating by users.
On the user side the blogging platforms, social network sites and wikis would need some way to add microformat support. See for example this plugin for wordpress (via F&L). If someone knows how to do the same for blogger please tell me in the comments. It needs to be something like clicking a button to link to a paper and out comes a formated hReview.
I think finding standards for manuscripts is a good start because a lot of people already tag and blog about papers. There is a lot of information to aggregate and a lot of interest in having a good measure of impact for individual papers. What we learn from putting this in place can later be used for other types of data communication (e-lab books). Another possible good start would be conferences and conference reports (related to hCalendar ?).
Of course, this would require the participation of science publishers. They are the ones best in place to set up the tools and expose some of the information in a structured way to help enforce a standard.