That depends on where the leaves, and stems, that are turning brown, dying or dead, are. If on the bottom of the plant that could indicate one of the wilts.
If in the middle of nice growth that indicates mechanical damage.

there is an incredibly active tomato forum ... i suggest you address the experts there ...

ken

You didn't mention which tomato forum is the active one...I've tried this message on the Tomato Pests and Diseases forum and not had one reply. I'll try the Growing Tomato forum and see what happens.

These problems mentioned aren't really ocurring in the lower parts of the plant(s). But I don't see any kind of mechanical damage that could be causing this problem, especially as it becomes more common as the season progresses.

Here's a photo of a different plant, an Early Girl. Look at the ridges/brownish areas on the tomato fruit, very strange. The leaves on this plant are doing the same thing, turning brown and crumbly.