I only took my 5 druids to 60 so far (and left 4 of them there), but a bear tank was quite good in instances, and healing was really very good when spread across all 4 other toons. (I leveled them 15->60 in instances only and they were my 1st multibox experience.)

However, I had two problems:
1) Casting a healing spell knocked them out of moonkin form.
2) Deciding whether to interrupt the DPS spell in order to start an emergency heal. (I can't remember how/if I dealt with this one atm.)

I suppose if I try this way again, I might try only one in moonkin form. I thought you only need one moonkin aura anyway, but ughmyheadhurtz made an interesting comment about survivability and mana that I didn't know about.

Bear tank + DPS moonkin + 3 combined DPS/Healer?
or..
Moonkin tank + 4 combined DPS/Healerform? (Dont forget that Moonkin gets good armour & health bonus)

If I do it, I will probably try Moonkin Tank, to see if Moonkin can hold threat against combined DPS/Healing spread over other toons. Talents + thorns + choice of spell (eg FF etc) might give enough of a gap for this to work well, but I have not actually tried it before.
There is an interesting article about tanking as moonkin here: http://forums.wow-europe.com/thread....05842304&sid=1


Instancing 15->60 with combined DPS/Healers the effect was very nice. 4xHOTs plus 4xsmall heals plus round-robin 'oh-sh1t' buttons made it very good, and the healing aggro was never a problem because it was spread out. It was also a nice way to learn multiboxing, since I only had to split my thoughts 2 ways instead of 3.
It sounds like that might not hold true 60->70->80, dunno. My new team is mid 70's, and I don't have experience of LK instances.

[Edit: lol at number of edits :p ]