Can zenphoto write title, description and tags to the EXIF fields of the image files themselves?

I'd like to use zenphoto for quite a large gallery, and it would make me feel much better if the data was in two places (the file and zenphoto's db).

I'm really liking zenphoto so far!

No, zenphoto only reads the data. You could/should use a program for adding the exif stuff before uploading in that case.