Matt Langford says:
There’s a new update for Tiny Theme that adds one of the most requested features. There’s now a separate plugin available that will enable summary/truncated posts on your home page instead of full posts. This is only triggered when your post has a title (meaning it will never summarize microposts).
The plugin requires Tiny Theme 1.5.1. It works automatically once enabled, there's not even a setting screen. All full length posts will be truncated. You can (optionally) choose the truncation point of a particular post by adding a more tag wherever you'd like.