Vietnam supplied around 1% of the coffee in the world around 1990 and
today produces around 12-14%.  Almost all of it is the cheaper robusta
type, which is easier to grow than the (also more expensive) arabica
type.
Could you trace a couple of good articles or pieces of research on the
causes of this massive increase in productivity ?

Alsinger,
The articles I were able to find are these. I hope I gave you the more
useful and pertinent articles and online sources for your needs.

Vietnam: Silent Global Coffee Power (INeedCoffee.com)
http://www.ineedcoffee.com/02/04/vietnam/

Orientations of Vietnam Coffee Industry
Speech by Mr. Doan Trieu Nhan
at International Coffee Conference
May 17-19, 2001 in London, UK
ftp://www.ico.org/event_pdfs/nhan.pdf 

Tea & Coffee 06/03 - Vietnamese Coffee and the Plight of the Montagnards
http://www.teaandcoffee.net/0603/special.htm

Dream of Vietnam's coffee king
http://perso.wanadoo.fr/patrick.guenin/cantho/vnnews/cofking.htm

Vietnam coffee industry - learning from the past!
http://www.new-agri.co.uk/02-6/develop/dev04.html

Tea & Coffee Asia---http://www.teacoffeeasia.com--- Coffee in Laos
http://www.teacoffeeasia.com/news.asp?id=505
--> Not about Vietnam, but may be related and helpful as Laos is in
the same general area.


Book suggestion:
Amazon.com - Coffee: A Dark History: Books: Antony Wild
http://www.amazon.com/gp/product/0393060713/002-2213102-3220826?v=glance&n=283155

Link to paid market research:
RTD Coffee in Vietnam - Research and Markets - Market Research Reports
http://www.researchandmarkets.com/reports/64385/
--> This is something you have to purchase to gain the information
from, but it may contain some essential history.

Hot Drinks in the Vietnam : Market Research Report
http://www.marketresearch.com/map/prod/1193530.html

Vietnam Investment Review - Coffee exports: brewing up success
http://www.findarticles.com/p/articles/mi_go1534/is_200407/ai_n6328374


Google Search terms used:
coffee market vietnam
coffee history vietnam
coffee research vietnam
coffee success vietnam

I hope this has been a helpful answer. If you need something
clarified, or have a problem with the answer, do please post a Request
for Clarification before rating and I'll come back to you as soon as I
can. Thank you.

I'd like to look into this for you (...after I go brew myself a nice
big pot of [potentially Vietnamese robusta-ish] joe.  Ah!  I think
I've just found export increase Cause No. 1:  Coffee craving is
similar to the pass-a-yawn-along phenomenon!  You mention it, I gotta
have it!  Alright, I'll stop cracking my C+ grade witticisms and get
to work....

One question first - were you hoping for articles within publications
of particular interest or familiarity to you?