It would depend on the state the leaves are in, I think, as well as the particular plant. Much of our nursery stock comes from much warmer places and may have leaves that are farther out than ones already growing here, and those may be susceptible to frost damage. Something with leaves that are particularly frost sensitive like Japanese maples or hostas I would definitely not plant out yet since it would probably lose all the leaves and might not have the reserves to regrow as well since it is young. In fact, if I already had bought the plants, I would probably put them all in a garden cart and wheel them to a suitable spot during the day, but then move them to a garage, porch, or basement at night for protection unless I was sure their new leaves were frost-hardy. Next week is supposed to be fairly cold and the there may be snow (Sunday's high temperature is predicted to be below freezing here) so I'd use caution. Mother Nature's April Fool's Day joke!

If it is local and is still bare-branched, you could plant it, but you might not gain anything unless your soil is warmer than mine.

Boston? I'd say as soon as this rain dries out a bit would be a great time to plant dormant or bare root shrubs. Most people wait too long to do that.