Over the last week or two, I have devoted some time to developing a systematic (and documented) set of APIs for querying and extracting data from Numishare. These advances have been applied to OCRE already and will be available in the new version of Mantis, due out in the near future. Moreover, since I have heard one or two requests about actually downloading data en masse from Mantis, I developed a rather simple PHP script which allows the user to do this. The PHP script has been added to the Numishare codebase in tools/get-ids.php. The comments of the script contain the basic execution instructions.
Documentation for Search API: http://wiki.numismatics.org/numishare:search
Documentation for Get API: http://wiki.numismatics.org/numishare:get
The Search API documentation details the two response formats (Atom and RSS) and the Lucene query Syntax (since the search results are derived from Solr). Most importantly, the wiki lists all of the fields which are used for searching and sorting and their data types, as well as several usage examples.