Potted perennials should be okay if they are kept watered and you are sensitive to keeping them either in the sun, if they are sun perennials, or in the shade if shade perennials. We have experienced such a delayed spring, that it would be best if the soil warms before planting so as not to shock the roots. However once this happends the sooner you can get them in the ground the better.
Chris

Most perennials are very hardy plants. I have kept some in plastic bags with drainage holes slashed in bottom all summer and planted out in the fall. They continue to grow in the bags so keeping them watered is important. As long as the roots don't dry out they should be okay.