I've found several of these guys in my small backyard garden:

http://xs.to/xs.php?h=xs840&d=09242&f=bug595.jpg

They resemble Colorado beetles, but are smaller (about 5-7mm) and
instead of long brown stripes have brown spots on their backs.
One of them was sitting on a grape leaf and I am pretty sure it was
eating it!

Who are these and how much should I be concerned? Besides grapes, I
grow some peppers, tomatoes, eggplants and herbs.

Thanks!