Zotero is already able to store DOIs for articles & is able to pass them to OpenURL resolvers. Do you have other things that you wish it could do with DOIs?
Depending on your OpenURL resolver, this should already happen when you press 'locate.' Many people can use crossref.org and/or ISI's 1cate as resolvers if their institutional resolver does not do this.
The new (Summer 2007) edition of the APA Style Guide to Electronic References makes using doi's in citations the preferred means of pointing to the source article.Without it, you have to deal with urls or database names. Scraping the doi's from the article databases and storing them in their own field then becomes very important.
* Clicking on DOI title opens http://dx.doi.org/[insert_DOI] , just as happens with URL
* If no URL exists, the "View" button brings one there.
see http://www.crossref.org/openurl_info.html for further info