I have a little bush which lost quite a few leaves due to overwatering. They are healthy looking and fragment. I wonder if I can use them in a similar way to kaffir lime leaves? I couldn't find much info re: toxicity, but lemon leaves are used in some regions to impart flavour .
This is Texas A&M University's description of calemondin: http://aggie-horticulture.tamu.edu/patiocitrus/Calamondin.html
In it, they seem to indicate that the leaves are not toxic:
The distilled oil of the leaves serves as a carminative with more potency than peppermint oil.
However, they list just about every use of the tree and its fruit, from marmalades to hair conditioner, and that's the only mention of the leaves. Because that's the only usage mentioned, I would suspect that even if the leaves are not toxic, they're not suited for flavoring anything.
I hope that's at least a little helpful.