If these holes look like something has taken miniature cookie cutters to your plants, then it is likely the work of leaf cutter bees. The holes are usually along the edges.

Here is a link that might be useful: {{gwi:10373}}

Or an irregular hole in the middle of the leaf might be slugs or snails.
Linda C

I should have posted these first since a pic is worth a lot of words :-)

Here is a link that might be useful: Petunia + Geranium Pictures

I also have small cookie cutter holes in my petunias which are in a large pot on our deck. They are in the center of the leaves and not on the edge. Tru Value guy thought it was earwigs, but I believe I see frask which I guess means worms? Comments? Suggestions?