I get asked about linking to entries in OpenWorldCat from time to time. Here is an update based on information from my colleague Mike Teets, who has overall responsibility for application development at OCLC.
There is now a link at the top right of each OWC page that allows direct bookmarking of the item "Bookmark This Page".
We plan to add, in the near term, a permalink to each page. This differs from the bookmarking in that it can be cut/pasted directly without going though bookmarking.
Current session-based URLs can in fact be cut and pasted, passed around, and so on. If we get a URL passed in with a session identifier that is expired, we direct the user to the correct page anyway. A little longer term, we will hide the session information on the URL altogether so it is more obvious that you can pass the URL around.