I decided to spec holy to get in groups. I was wondering if you had any guidelines in terms of what stats to shoot for, for heroics. Right now I'm about 1100 +spell, 15% crit, 115 mp5 (without BoW). From what I've read on EJ I should be stacking int wherever possible, but I feel like my mp5 is really low. Although I have so much mana (13k unbuffed) I'm not sure running out is an issue, unless the fight goes beyond 5 minutes.
I did manage to heal heroic UK with two early wipes due mostly to my newbness (remembering to use Lay of Hands would have prevented both). I just got the feeling that I was undergeared while running it because I was really struggling to keep up with the tank on most pulls and I rarely ever had time to heal anyone else taking damage.
I haven't really healed with the new 3.0 talents, so take what I say with a grain of salt.
EJ focuses on Int because both Replenishment and Divine Plea work of 'Total' Mana. So if you increase your Total Mana, you regenerate more. Add to that the extra spellpower and crit, and you can see why EJ is promoting Int over Mp5. Now, in a heroic, you might not have Replenishment, and you might not use Divine Plea as often, since the fights are shorter. So the value of Int is less.
However, looking at your stats, I think you need more +healing. EJ kind of takes it for granted that you are trying to stack as much +heal as possible, even if they don't explicitly mention it. 1100 seems rather low for an 80 attempting heroics. I would really focus on +heal, and not worry about regen as much.
As for the situation you are having trouble with, that's what Beacon of Light was made for. It's a new tool, so it will require practice. But try and keep it on the tank as much as you can, especially in boss fights. It will allow you to heal the other party members and still keep the tank up.
Remember to Judge (use a focus macro) to keep the Haste bonus up.
/cast [target=focus] Judgement of Light
(You can set your focus with the /focus command, or bind it to a key in the Options menu.)
Also, I would advise using the glyphed Seal of Light, as that would make your spells more powerful. You sound to me like you are fine with managing your mana, but you need your heals to be more powerful, to do more healing-per-second. The cure for that is more +heal, and to a lesser extent, more +haste.