> Is it RESTful to add GET parameters
> to a collection in order to add
> functionality such as filtering,
> sorting, or pagination?

They're not actually called GET parameters, they're called query parameters. PHP actually has it wrong on that subject ;) Anyway, yes, I'd imagine that is the best way to do it. In REST-ful applications, the URI must represent a resource (an a collection of resources is, in and on itself, a resource). The filtering solution twitter (and others) use is elegant, but if you want it to sort in a certain way, there is no other way than passing it in the query string, without violating the "A URI is a resource" mantra. I don't think it's a bad thing to do so.