Inspired by the Google Scholar OpenURL Firefox extension/bookmarklet, here's a -->LocalOpenURL<-- bookmarklet that replaces the default OpenURL links in HubMed pages like this one with one of those big ugly OpenURL buttons pointing to your local resolver (in this case the University of Alberta, but it should be easy to edit the code to point to your local OpenURL resolving service).
Also, here's a -->LocalSFX<-- bookmarklet that replaces the default SFX and PubMed links in HubMed pages to point to local services (in this case the University of Manitoba, but again it's easy to alter the variables to point to any service).
The problem illustrated by these bookmarklets and the Firefox extension mentioned above (which these could easily be incorporated into), is that they have to be specially tailored for each service (Google Scholar, HubMed, etc). As Daniel Chudnov and Jeremy Frumkin have begun to illustrate in their paper Service Autodiscovery for Rapid Information Movement, there really needs to be a standard way of adding enough metadata to pages to generate OpenURL links from a single bookmarklet or Firefox extension. They suggest using mod_context embedded in XHTML, or use of a 'link rel=' tag to denote OpenURL links.
This is similar to the problem of needing metadata exposed in online text, so that you can select a block of text and store this along with automatically-generated bibliographic data. The same as for an OpenURL link, this needs author, title, source, date and volume/issue/page metadata to be exposed, so perhaps Dublin Core or MODS would be useful for both these ideas?