Since a bibliography plugin/add-in is not a word processor, I won't include them in the review, and in fact, its complexity begs a mini-review or review unto itself. I do know that Word 2007's citation feature was perhaps the most debated topic for its beta. We all wanted it to work like EndNote, since its UI made so much sense. But once again, Microsoft went off and did its own thing, reinvented it, and immediately ran into a lot of problems which never got fixed. Microsoft did not understand the importance of this feature to the adoption of Word 2007, in my opinion, as they discarded virtually every suggestion and offer for help. So I urge others NOT to depend on the citation feature in Word 2007. OpenOffice's Base can be used for the same purpose, but you have to build it to suit your fields. You can also customize the layout in OpenOffice's Bibliography Database feature. Some academic departments have written plugin forms for OpenOffice, however.
Another consideration to building such an app would be that the various fields are constantly shifting and updating their formats every 3-5 years. Such a project would require a team to keep up with the changes and implement them, creating a huge time sink.