Coop pointed out in the last post that one of the troubles with healing in SWTOR is the UI. But it's not just a SWTOR problem. Almost every MMO I've played has featured a DPS-centric default UI.
Which is rather odd if you consider the fact that healers are the one role which interacts with the UI the most. One would think that the default UI should be optimized for healing. A healing-centric UI would still be functional for the DPS and tanks.
Here are three elements that a good healing UI needs:
1. All the friendly health bars in one place.
Almost all health bars put your own health bar in a different location than the other friendly players. SWTOR puts the companion health bar in a completely different place too. This is the first thing which is fixed by every single healing mod. All relevant health bars are collected together in one compact location.
2. Minimize target-switching.
I would love to see a default UI implement mouse-over casting for friendly spells out of the box. It makes healing so much easier and cleaner.
I also rather liked having Warhammer Online's use of one friendly target and one hostile target, that could be switched independently. You can kind of work around this with focus targets, but it's a lot easier to keep an eye on enemies with true dual-targets.
3. Emphasize relevant debuffs and buffs.
This is the hardest element to get correct for a default UI. But simply displaying all buffs and debuffs on a target is just not good enough. A healer needs to know when important debuffs are on the target, especially for dispelling. As for buffs, in general you only need to know when your short term buffs like HoTs and shields have worn off a friendly target.
I strongly recommend that any new MMO design the default UI with healers in mind. In fact, I'd go so far as to insist that the default UI designer be a full-time healer. Healers are the class which will interact with the UI the most, and thus the ones who suffer the most with a badly-designed UI.