I love regen ever so much. On demon wall 90% of my healing is from regen and medica II's regen.

The main things to note about using regen, unless you know your tank will click off regen before he pulls (very few will, and I often tell the ones I'm in mumble with to remove it right before they pull) don't cast it when the last mob has about 1/4 to 1/2 their life left.

Regen is excellent to place on people you know won't be taking damage again for a while, throw it up on them and focus back on the tank. And its especially useful on warrior tanks place it and stoneskin on a warrior and you may not need to cure at all unless a lot is going on.