Lines will be smoothed, similar to how the Bamboo iPad app does it. Our prototype already does that. Does this answer your question?

You'll be able to create custom (even grouped) widgets and store them for easy access (e.g. if they're complicated to draw every time). We also plan to make pentotype even recognize your custom elements.

Clients won't need to install anything because pentotype is web-based. They just can point their browser at a URL and interact with the wireframe and leave comments.