Plone with external web services
Plone conference 2010
The clear sign of mature product is when you realize it can't do everything and it is much better to use the best tool for the job then reinvent and try to shoehorn everything into Plone.
Restful search
Calvin Hendryx-Parker from Six Feet Up told us how they have integrated Solr into Plone. In his talk Enterprise Search in Plone using Solr he explains how alm.solrindex plays very well with ZCatalog and you don't have to do any changes to your code, just install it as a normal ZCatalog index.
David Glick from Groundwire went through the technical aspects of how to use web services from Zope/Plone. In his talk The Art of Integrating Plone with web services he mentions REST, XML-RPC, and SOAP. The interesting thing is that Zope has had XML-RPC support over 10 years! You have been able to provide and consume web services with Zope and Plone for many years.
Diazo the theming service
Me, Sasha Vinčić did a presentation External E-commerce and Plone playing along where I presented how you can use external e-commerce and I also mentioned that you can look at the theme as a service. With the tools Deliverance and Diazo(former XDV) we are able to see it as a service. As with many services we get the benefits of being able to exchange it and reuse it across other services. Easier and faster Plone theming with Deliverance and xdv by Nate Aune, Jazkarta and Theming with XDV by Laurence Rowe and Diazo will be the default theming in Plone 5 indicates that this is the way to go, see themes a service.
How do you use web services with Plone or provide them from Plone/Zope?