Thanks Lorna.
Looking at replies below (and I don't know much about script hijacking), I think I will stick setting application/json in the http-header. And if I am writing a server I will (try) not accept simple plain/text.
Ohh BTW, I learned a lot from the slides that you linked in this post. I asked my colleague to read slide 39 - 42 for a quick introduction to SOAP. Pretty interesting stuff !