More recently I found this great blog post. Which is great for the cases like Tony and where you really want to post something in your cuke:
For my case this became:
def send_log(file, project)
proj = Project.find(:first, :conditions => "name="#{project}"")
f = File.new(File.join(::Rails.root.to_s, file))
page.driver.post("projects/" + proj.id.to_s + "/log?upload_path=" + f.to_path)
page.driver.status_code.should eql 200
end