Blossom End Rot
One of the biggest problems with tomatoes is that nasty black crack on the bottom. It's blossom end rot and caused by a calcium deficiency. Make sure the nutrition of the soil is correct. But even if everything has been done correctly from a nutritional standpoint blossom end rot can be a problem. Calcium is a water soluble nutrient. If you don't maintain proper watering conditions, the calcium is carried into the root system of the plant with the water. So if you run your beds dry and your plants do fruit, you can still get blossom end rot and that basically is a water deficiency, not a calcium deficiency. But they are related.
Another consideration - Overhead watering can be a problem. Different plants have different watering needs. Watering at the base of the plant allows you to water the root system not the leaves. The leaves don't need that much water, they'll take it up from the roots. If watering overhead and there is disease on the plant it will splash the disease around to other plants, the other tomatoes. So avoid overhead watering, give each plant the correct amount of water but apply the water at the roots.