When it comes to backups, I’m certainly not perfect, but most of the good ideas I read online are put into practice in my setup. I use Dropbox, Time Machine, SuperDuper and multiple computers, so I feel my data is pretty secure.
When it comes to my website, even though Squarespace are awesome, I feel obligated to store some kind of backup of my data myself. For this reason, every two weeks, I export my blog’s content and store it in Dropbox. It takes about a minute to do and is certainly worth the time.
The XML file Squarespace generates is fine for importing into a WordPress installation, although I have no plans to do so. Opening the file in a text editor and performing a search is likely the only use I’ll have for this feature, but I enjoy knowing it’s possible. Squarespace supports importing from WordPress, so I have to imagine an exported WordPress XML file created by Squarespace is 100% supported by Squarespace when importing. I will test this out myself.
If you use Squarespace, I highly recommend performing this export as often as you think necessary — just in case Squarespace happens to lose your data.