A site I built was launch today for Matthew Good's wife Raeleigh. Matt designed the site which is a total copy of a popular Squarespace template, but with certain customized elements that were extremely difficult to implement with the actual template. When something is difficult to tweak....Matt and I build it from scratch using the Squarespace developer platform, which basically is a blank white page with no custom font, sizes, or colours. We did the same thing with his current site. There are only a few subtle design tweaks compared to the original template, like taking away the rounded corners on elements, changing the share button and blogging meta-data. The biggest addition is a header that sits only above the content that has Rae's twitter widget. Little things like that are next to impossible to implement without building it yourself.
I seriously love building with the developer platform.
I learned quickly that when you use the developer platform there is no "mobile" navigation menu, but recently I've gotten quite good at implementing them with minimal code. Simple things that this excite me. I am truly a dork.
If you want a custom Squarespace site built visit Sites Made Simple and I'll build you one.
Update: Totally just realized I'm using the template mentioned above. This site is not done with the developer platform, it is just a tweak of the template (limited to built in Squarepace options). I don't get enough traffic to design this site in a unique way ;-)