They dig and make a huge mess of the mulch in my front bed by the house. I'm pretty sure they have nibbled on some plant stems but haven't ever caught one at it. I can hear them chittering and scurrying in the underbrush while I'm weeding (at least I hope its just chipmunks doing that).

Well they can be a real pain. They will nibble and breed like crazy,so soon you are overrun with them. But Chipmunks are soooo cute right? LOL

Thy will dig and tunnel all over your garden. Most especially around any hardscape. They love rocks. They eat more perennials than veggie plants in my home and work gardens. I have found that liquid fence is a fairly good deterent.
Also they are usually thick with fleas so if you have fleas in your area, you will see an increase in your population. They will try to run off birds etc. Very territorial.

Yes, the tunneling is a real pain. I have one living under a rosebush right now. The holes can damage roots and kill plants. They also come into the veggie garden and make off with whole cherry tomatoes. This is actually better than them chewing bits off the bigger ones and wasting them. I often see tomato seeds and skins scattered along the stone wall where they like to live. I usually find I have enough tomatoes to "share" but hopefully I won't change my mind this year- seems like a bumper crop of chipmunks. I haven't noticed damage to other crops I grow (mainly herbs and peppers).