I'm considering storing the URI for a workitem from our TFS environment in our helpdesk system, however looking at the URIs TFS gives us (vstfs:///WorkItemTracking/WorkItem/327), there doesn't appear any recognition of which team project it is associated with, which makes me wonder how meaningful they are?
Is it possible to load a workitem by just URI? Or will I have to store the Project URI as well?
The work item URI is unique across the Team Foundation Server in TFS 2008/2005 or across the entire Project Collection in TFS 2010 (TFS 2010 has a new notion of project collections - see here for more information). The Team Project that it is in does not affect the ID.
Therefore to have a unique reference to the work item so that you'll always be able to get to it in the future you need a TFS server URI and a Work Item URI (i.e. http://tfsserver:8080/ + vstfs:///WorkItemTracking/WorkItem/327)
If you will only ever have a single TFS server or a single TFS project collection in TFS 2010 that your CRM system is attached to then you can assume all work items are linked to a single TFS Url.