One of the big debates these days when it comes to cloud computing center around portability and interoperatbilty between providers. That is, if you build an application on Amazon's EC2 or Google's AppEngine or Force.com, or store your data on Box.net or Amazon's S3, how hard is it to port your application or move your data to another cloud provider? If you develop on a given platform, how locked-in, or not, are you? And beyond that, could developers benefit from having standardized APIs to develop to without having to learn a new model and interface each time. As you'd expect, there's no easy answer to this.
Webhooks offer a far more efficient way to monitor changes to an endpoint than traditional polling. In this recent article on InfoWorld, Mark Geene discusses the technology and highlights three commercial implementations that put it to good use to improve the customer experience.