Recent-ish WebKit and Firefox browsers do support PUT and DELETE in XHR requests. I'm pretty sure that any IE < 9 does not, not sure about IE 9 or Opera (though I'd guess Opera does support those verbs).
one major problem is HTML forms doesn't have a way to generate these.
I could invent one pretty easily. Instead of <form action="post">, it could be <form action="put">.