I've spent some time over the last week, and I have completed an initial pass at writing an OAuth Consumer in PHP5. I'm biased, but it's a nice chunk of code capable of fairly routine POST based OAuth requests using either an Authorized header, or a raw url encoded POST request body. My main remaining task is final cleanup, included refactoring, rolling my final set of acceptance tests into PHPUnit from SimpleTest, and adding support for HTTP GET, RSA, and a storage API so tokens can be saved in the background rather than outside the API.
Example code is included showing how to connect to the ma.gnolia bookmarking service and grabbing the response body from the request. He has a few more things to finish up before it's ready to go (backend storage, reworking the handling of web service API interaction, etc).