If you are checking your plants daily to see if they require water (which is recommended for new plants) there are signs they offer that water is required.  If you look at the new growth on the preceding pictures, you will see that there is a distinctive hook downward that will show itself prior to injury. If water is applied at this stage, often the plant's stems will rebound and become upright again - and no injury will occur. If this stage is left to go too long, then sometimes the tissue will become damaged.

This scorch injury is marked with brown dead areas that appear between the veins (as on the redbud picture shown here) or at the edges of the tissue. If the leaves are small, they may curl up completely and fall off. There is a distinct 'crunchy' characteristic to the leaf. This is a little different than what is sometimes seen with a fungal condition, as fungi spots usually have a yellowish 'halo' around the dead areas.
Japanese maples are plants that don't like a lot of inconsistency in their soil moisture, and scorch can appear readily and fairly quickly afterward. In the case of the example here, the sunniest side of the plant gave off more moisture than the shady side, and that's where the scorch injury appeared first.

While it might look terrible, if the damaged leaves are removed in spring or early summer, there is usually sufficient time for new leaves to appear yet this season. Even partially damaged leaves continue to process food, so removal should be dictated by how much is damaged.  Nipping the tip of the shoot off is advisable as the plant will break new leaves more quickly. A few weeks more of warm weather, with moisture, and the plant will be budding new leaves again from the latent (backup) leaf buds that are already on the plant (as you can see).

Here are some tips of things you can do to minimize leaf scorch, and assist your plants if this happens to you.

1) Change your watering method. If you are not sure of how you should be watering your new plants, click here.  Deeper is always better than a little bit more. Ensure that you have a decent saucer to retain moisture around the base of your new plant (as below). Where heavy soils are present, you will likely find that the time frame between waterings may be a little longer.
2) Consider cutting back the plant. This is done to lessen the draw of moisture that the plant requires. In order to keep watering requirements low, at Grobe's we prune many shrubs and evergreens in late June to mid-July.  If there is injury, and the plant is a vigorous grower, the regrowth will be quicker than the Japanese maple example above. An example of this type of transformation is detailed here.
In the case of evergreens, it should be noted that the oldest needles will usually drop out of the plant (much like a Christmas tree drops its needles first when dry from the inside). If the tree is so dry as to cause injury to the new growth, then it's possible that recovery will be more difficult, and aesthetic damage will have taken place. Some plants, like spruce, when dry will rain needles that will never come back.

3) Feed your plants. Now you have to be a bit careful with this, as too much fertilizer with this kind of heat isn't advantageous either, but a little bit of water soluble plant food will help the plant to produce more leaves when the weather breaks.