Hi rgusaas... From what I can tell, if you are using a "known application" (e.g. Word, Excel, Powerpoint) then there is an automatic checkout feature whenever someone opens the document for editing from within Workspace. But I don't know of anyway to "checkout" a document for local editing. It would be a great feature to have - and is really a requirement when dealing with "unknown" applications. Otherwise you could have two people editing the document at the same time and end up with conflicts.
Hopefully document checkout will be something the Workspace team will add. It would be nice if they also checked out the document and opened it in your local editing program of choice.
-Norm