I would first like to say that I love the concept of Squarespace, and think the control panel, analytics and pricing are all fantastic. However, the execution is a bit off target, and the example sites for each template are misleading. It is impossible to get your site to look like the example sites without modifying the CSS, with the sidebars in particular being a problem.
Examples include: ugly bullet points in the tag index, poor spacing on section headers, bad font sizing and spacing on taglines and site descriptions, clipped images in sidebar, I could go on.
Support have been very friendly and responsive, but can suggest no better solutions than applying custom CSS, which is of course "not supported".
Unusable for us in its current form, but would definitely be back if these issues were resolved.