Although it's not directly about RAW, Fazal Majid wrote a post in April about how to work around the extra baggage (XMP data) that Photoshop drapes around its image files.
For Majid's workflow, there's a bug that renders the data innacurate in his photos, and he also traced it to a bug that renders images invisible in Internet Explorer. He uses a few open source programs and even wrote one himself to deal with the bugs:
I wrote jpegstrip.c, a short C program to strip out Photoshop's unnecessary tags, and other optional JPEG "markers" from JPEG files, like the optional "restart" markers that allow a JPEG decoder to recover if the data was corrupted — it's not really a file format's job to mitigate corruption, more TCP's or the filesystem's.
If you're having problems or frustrations with XMP data (or just want to strip it) the post is worth a look-see.