It's interesting to see the decision making process at organizations evaluating geospatial technologies. One area that I see a lot of "effort" from an IT and developer stakeholders in Geospatial Software Purchases is in the form, function and ROI of the technologies REST or SOAP. This is being driven on the enterprise side of the house where these technologies are essentially thier choice of which to invest in.
The ESRI Developer Summit Keynote provides a good technology overview by Dave Chappel on "SOAP vs. REST". Probably for people at a decision maker level trying to understand the technology and "keywords" or end users trying to get a better understanding of the technology, this is a good starting point.
Two areas that is always analyzed and heavily weighed in any evaluations is INTEROPERABILIY and SECURITY, and this is where SOAP clearly becomes the "leader of the pack" in technologies today. This is with any technology that these two categories are scrutinized. The requirement for proprietary REST client interfaces is such a drawback of the technology. Why would I want to have to integrate a proprietary interface in everything that I want geospatial data and have a proprietary client interface integration effort to 'work' with my GI and services? The pushback in that process is definately "loud and clear" from the market. In terms of security, you CAN secure REST endpoints, this is not a problem, but a lack of any standard to do so and/or the client interfaces proper ability to handle security rhealms must be accounted for, you shouldn't have to 'poke' at it to find out if it works. Again, same theme, proprietary is a big blocking issue there.
Mr. Chappell raises a good point in that SOAP is not "easy" to manage from the client side of the house as managing XML isn't the easiest or most eloquent. Fortunately in the GI space, everybody already supports the standardized services (WMS, WCS, WFS, etc, etc), so the "effort" and ability to handle it with standard interoperable client interfaces is widely prolifererated and highly available, so i think that point is rather 'mute'.
Don't get me wrong, REST is a GREAT technology, it simply needs some standards bodies to define how and where they will be used to get the same ROI and proliferation as the well defined SOAP services today. This process is firing up with the OGC right now. Hope the conjur up something useful with that... :)