Having weathered the coldest night of this snap we are experiencing, I can say that our established plants have suffered worse damage than the new ones we bought so far this spring. I've either covered the new ones (and a few established ones that I was concerned about) or brought the ones not planted yet in the house at night.
Of the established plants, so far we've got a lot of frost-bitten holly bushes, some yellowing evergreens, and to my sadness, some damaged wood iris blooms (which I had covered). The most dramatic casualty so far is a butterfly bush we've had for a couple of years. It's all burned, and I don't know whether it can be saved. However, most of the established plants will survive, I think.
The new plants that I put in the past three weeks are doing okay, with some leaf burns along on the limbs and leaves that rested up against the sheets I was using for insulation. Most of those shrubs seem largely fine. My riskier plantings, the gerbera daisies that I put in a couple of weeks ago, are in good shape (I covered them each with thin plastic pots and pillow cases, over which I threw a sheet).
Two more cold nights of covering and moving plants to go, but I feel much better about our prospects now than I did 48 hours ago.