The designed downtime worries me some. I always want to punch people in the face that use this word, but I have to say I think the downtime is something that has to arise organically from the game world and not be a heavy handed implementation.
The good way to put in downtime is increasing the stealth elements of gameplay in the 'player versus world' concept. In other words requiring timing and care in splitting mobs, avoiding unnecessary encounters, and laying out a plan of attack (in other words, a period of 'mentation' that encourages social aspects and also will be a nice break from the general repetitiveness of combat).
Downtime should also be a negotiable element, one which can be chipped away at by the right group who knows what they're doing. This will happen naturally if downtime is implemented in the above manner.
Bad downtime would be stupid shit like incredibly and needlessly long recast/reuse timers on important combat or healing spells, or other artificial design implementations which are clearly the only to forcibly prolong your downtime, and which cannot be avoided by any means.