What is a Manifest in Scala and when do you need it?

Since Scala 2.7.2 there is something called Manifest which is a workaround for Java's type erasure. But how does Manifest work exactly and why / when do you need to use it?

The blog post Manifests: Reified Types by Jorge Ortiz explains some of it, but it doesn't explain how to use it together with context bounds.

Also, what is ClassManifest, what's the difference with Manifest?

I have some code (part of a larger program, can't easily include it here) that has some warnings with regard to type erasure; I suspect I can solve these by using manifests, but I'm not sure exactly how.