What kinds of tomatoes are they? There are many varieties that radial cracking is normal on (crackes from the stem out, like a wagon wheel). It usually happens after a sudden uptake of water, such as after a soaking rain or from overwatering. A very heavy rain after some very hot weather, in particular can bring it on.
There isn't really too much you can do about it. You can harvest your not-yet-ripe tomatoes a little early if you are expecting a big rain. Other than that, some varieties are more prone to cracking than others. You can use this as a factor in choosing what to plant next year. Personally, a little cracking doesn't bother me. The fruits are still edible -- they just may not look very pretty.
Most often it something is eating your fruit, you will be able to tell. There will be very definate teeth marks. I have one tomato that is almost ripe, so I have left it alone waiting patiently. Well, I went out to pick it yesterday and some darn little varment has gotten to it.
As for the dark spots, I am not as familiar with them. Here is an awesome site though that answers many MANY questions on tomatoes. Take a look through and see if any sound like the issue you are having. Tomato Questions
Hope this helps! This is my first year with tomatoes also, and I had almost given up. Now I have them coming out of my ears! Good Luck with yours