Over at Make they have a very useful article on Understanding Saw Blade Essentials.
You might think there’s not a lot to know before buying a blade for a circular saw, table, or radial arm saw, but when you look into it, your choices can be intimidating. Once you know a few basic terms and what they mean, and a few things about blade materials, types of teeth, tooth count, and a few other technical tidbits, you should be fine.
Here are a few terms and considerations you need to know in choosing a blade:
Some very useful hints and tips.