Every bit of advice that I get says that the Dutch give you about two years to learn the language; after that, why bother to make the effort of speaking English if you won't make the effort to learn Dutch? As the expatriates drain out of my corporate division here, there is definitely a reversion towards using Dutch in meetings and casual conversation. I feel like I get about a quarter of the words directly, and can infer about half of what is going on, gaining a bit each week.
'Still, it's hard to get up in the morning and keep the commitment to reading De Gelderlander, or to listening to Dutch radio in the car driving to work, or to Laura Speaks Dutch podcasts in the evening, a grammar book on the exercise bike, or to flashcards using VTrain and a session with Rosetta Stone in the evenings (now available online).
You get the idea... So immersion makes a lot of sense for me. Regina Coeli, the legendary "Nuns from Vught" is a good solution. The week costs about 3000 euro's, not too bad compared to 500 euros for ten two-hour group-conversational sessions at the local language school. For the cost, you get very high-quality, individual, 13-hour-a-day, five-day immersion. No shortcuts, no English: just solid Dutch conversation, grammar, and vocabulary training. The common course is two weeks, one week, followed by a break of a month, then another. The waiting list is six months long, so you should anticipate your needs early for your assignment.
The day goes from 8 am to 9 pm, consisting of alternating hours: individual conversation with a teacher, then language lab practice using books and exercises, then back to a teacher. Lunch and dinner includes "Taaltafels", and there are individual study breaks and group sessions with games and role playing. Instructors vary from demanding conversationalists to relaxed grammarians to encouraging mentors. (Somehow, I always got the demanding conversationalist at 9 am). Beginners use a series of exercises in a workbook featuring the exploits of Rob and Mariolein; advanced students have more traditional paragraph-level reading and writing. I was able to go through the workbook at about 1 1/2 chapters per day, two weeks easily finished the 10 chapters.
I thought that the experience was extremely effective: I could read a newspaper and hold a simple conversation to check out of a store or into a restaurant after one week. The instructors were first-rate and there is constant feedback on how you are doing. My pronounciation and grammar were very good coming out of the course, but you will need to continue to develop vocabulary and an 'ear' for parsing words in spoken Dutch (which always seems run-together to me). It's hard to find good follow-up, though: you can lose what you learned very quickly if you don't put it to use, and simple conversations with clerks and colleagues don't help much. I signed up for a conversational course here in town (I'm headed there now), but it is at a lower level and not as effective. Still, it forces me to keep developing, which is what the Dutch expect to see and appreciate.
And, no, the actual nuns left long ago...