It really depends on the webservice. Some are pure REST but most are REST-RPC hybrids. Although the examples are mostly ruby and python, I would recommend RESTful Webservices.

So what would a REST call look like in perl? Well, if you install lwp-request, from the command line, it may look like:

$ GET -e http://foo.bar.com/something
[download]

If you're really lucky, there may all ready be a CPAN module for the service (Net::Amazon::S3). If you're going to write a REST client, LWP and XML::LibXML (or another XML parser) are going to be your friends. If you're going to write a pure rest service, CGI::Simple is the only module to support the http PUT method (I provided a patch to CGI but that hasn't made it's way to CPAN yet).

You may be able to proceed with LWP::Simple calls (assuming stateless operations). LWP::Simple::Post may be needed *if* you know the right parameters, but I've had marginal luck getting the latter to function, so YMMV.

If you need to PUT or DELETE, you'll have to dig into LWP::UserAgent and HTTP::Request.

And once you've gotten your response to any of the above, you'll need a suitably capable XML processor...if you're lucky, just XML::Simple (if you're really lucky, just some crafty regexen).

FWIW: DBD::Amazon is REST based and, by far, that was the easiest part of the package development. I'm always amazed at the BFD that is made over SOAP interfaces. I guess the Java/Web Services crowd can't abide a solution that's less then a KLOC.

Go REST, young man, go REST!