Wow that's a lot of acronyms!
If you're following any academic library listserv, you've seen a lot of discussion and frustration regarding the APA 6th edition's treatment of electronic articles, DOI's, URL's and the like. A recent post to ILI-L linked to the APA Style Blog, which I plan on adding to my Google Reader. Today's post provides a flowchart (I kid you not, this is what citation has come to!!) for when to use a DOI and/or URL. I haven't pored over it, but it will probably be a useful resource to have on hand at some point.