As you can see from the variety of replies, it really is a subjective topic and heavily dependent on your play style.
If for some reason I am playing my DNC for missions or Aby content, I often find myself off-tanking if something bad happens to the tank, or if there is no tank to begin with. Most of the tanks I work with are Tarus, so their HP is naturally on the low-end and one nicely timed TP move can sometimes kill them in one hit. Fan Dance also has a lot of use when it comes to mobs with really powerful physical TP moves that I know I will need to mitigate if for some reason they eat throw my shadows. I have Fan Dance a full 5/5 because resetting the -pdt % ASAP is very useful for ME (and maybe not others).
However, if you find yourself being called into more damage dealing roles, Saber Dance will probably be more beneficial to you. I personally have one merit point in Saber Dance because it is superb but I usually am required to throw in additional heals every now and then, and constantly canceling saber dance is just not worth it to ME.
Probably the most controversial merits is No Foot Rise, which I have 3/5 merits put in. I personally cannot find the nerve to let go of the instant TP it provides. Many will argue 2/5 at MOST, since Presto+Step will put you at 5 finishing moves, but I prefer three simply because it gives more TP. With Reverse Flourish fully merited and +1 Charis Hands I get roughly 52TP, which is enough TP for a quick Curing Waltz III. Being able to do this has been very priceless to me. Also, many BCNM battles/missions will not wipe finishing moves upon entering, so using No Foot Rise twice before entering will allow you to instantly reverse flourish with 5 finishing moves before engaging the enemy. It's extremely useful to me, but if you don't think it sounds that great then obviously it is not the merit for you.
I don't have much to comment on closed position but I do have two points put in it.
The best advice anyone could give you is to pick what you THINK may be useful, and then go use it and decide for yourself. Merit points are so easy to get these days that experimentation should be encouraged, in my opinion.
Edited, Jul 1st 2011 2:11am by Tandava