Survivors Instinct - 'rate of X' means one hit points is regenerated every X seconds. I put one skill point in at level 12; whenever I went to store loot, trade or talk to NPCs my health could be full again by the time I finished. Not particularly useful, but handy once in awhile. I maxed the skill in the wastelands to use up some spare skill points, and this was pretty much the only healing I needed for the rest of the game (I used 3 minor restoration potions - one for Moriendor, two for the Demon of Lies).
Heaven's Gift - If you have Alchemy, one normal health + mana potion (need level 3 of heaven's Gift for this, IIRC) will give you a
restoration potion to completely re-fill your mana, so this skill can be repeatedly cast for as long as your right mouse button holds out. Some people find this very handy if they frequently run out of potions or money, but I found it too slow (in a test save), since I had no problems coming up with either by other means.
I have not tried Embrace Shadows.