Will Evans shows us how he sketches and wireframes interfaces in this cool video, which is a nice preview of what you may see in his upcoming talk on "The Right Way to Wireframe" at IXD10. Incidentally, he's using OmniGraffle with our free wireframe stencils. Will says this about wireframing:

Increasingly, as designers of interactive systems (spaces, processes and products for people), we find ourselves stretching the limits of communication tools to explore and document what it will be like to interact with the things we design.

We describe wireframing as a form of design communication that enables stakeholders, team members, users and clients to gain first-hand appreciation of existing or future problem spaces and solutions.

We create wireframes to inform both design process and design decisions. Wireframes range from sketches and different kind of models at various levels of fidelity looks like, behaves like, works like to explore and communicate propositions about the design and its context.

We think that the wireframing strategies user experience designers use are often constrained by the tools they feel most comfortable with: problem space, domain, expertise, theme, context of problem, bias towards types of design tools and documents, timeliness of artifacts created. For this reason, a session that attacks one business problem from the perspective of four different designers will provide attendees with a unique understanding and set of strategies and tactics to improve their own practice.