The slides for this presentation are available. No summary can do proper justice to this presentation so I'd suggest viewing the slides.
Sam's talk focuses on the various gotchas facing developers building applications using REST or Plain old XML over HTTP (POX). The top issues include unicode (both in URIs and XML), escaped HTML in XML content and QNames in XML content. A lot of these gotchas are due to specs containing inconsistencies with other specs or in some cases flat out contradictions. Sam felt that there is an onus on spec writers to accept the responsibility that they are responsible for interop and act accordingly.
At the end of the talk Sam suggested that people doing REST/POX would probably be better of using SOAP since toolkits took care of such issues for them. I found this amusing given that the previous talk was by Nelson Minar saying the exact opposite and suggesting that some people using SOAP should probably look at REST.
The one thing I did get out of both talks is that there currently isn't any good guidance on when to use SOAP+WSDL vs. when to use REST or POX in the industry. I see that Joshua Allen has a post entitled The War is Over (WS-* vs. POX/HTTP) which is a good start but needs fleshing out. I'll probably look at putting pen to paper about this in a few months.