I have a summoner who has an eidolon with the Spines ability from here. The '# of spines = Max Natural Attacks number' (so 4 at level 6, and 5 at 9th), coupled with it being a natural attack (so Full BAB), and it being a standard action has proven to be too much. It's limited to 24 spines a day, but that's enough to go through most combats, and take down the people I want *fast*.
Although, due to the ambiguity of the text, we had to make a few assumptions about the intent. Since they're natural, and the follow the limit of natural attacks per round, they were natural weapons. Since they were natural weapons, and since the force that you fling them at would matter, they add Strength, like a throwing axe would.
Since my eidolon has 18 Strength, that's 1d6+4 damage at least. With Arcane Strike added, that's 1d6+6, and then throw in Energy Attacks (acid) for a total of 2d6+6, and we're hitting 52 damage on average, since chances are I'm going to hit.
If you could clarify the ability a bit, that might help.