Greg Beaver has a quick look at what he says is "how not to upgrade PEAR" on your PHP distribution.

Just a few minutes ago, I was attempting to downgrade my existing PEAR to an earlier version so that I might be able to test a few things.

I figured I would get the 1.4.0a12. Unfortunately, I forgot that my preferred_state was set to "stable" and ignored the error message, trying again. Halfway through, I realized my mistake - I was upgrading to 1.3.6, which would bork everything. So, I reflexively hit Ctrl-C. Uh-oh. A quick peek at the disk revealed that I had hosed the entire installation.

Moral of the story?

It doesn't matter how experienced you are with a program, read the damn error messages and prompts!

Speed + not reading = very, very bad things...