It has been possible to add forms to sidebars in Sitemason templates all along. However, once the form is submitted, the user is taken to a confirmation page away from whatever page they were on. When it comes to just a simple contact form or quick survey, it would be a whole lot better to have the form submit (or show errors if necessary) in the same location on the original page. It can be done with hacks like using an iframe, but that has its drawbacks.
Chip Hayner of CentreSource just asked for a better way, so I added an option to the Custom Form to submit in place. Chip used the feature in Nashville Office Furniture's website to allow people to submit info about projects. If you were to fill out the form (and please don't unless you really want to submit a project), you would see the confirmation page in the same location.