The latest fixes and improvements to Default Folder X are now officially available in version 4.1.1.
The changes are mostly compatibility and bug fixes, but a side effect of one of them has been to speed up the login process in a lot of cases. DFX was asking the Finder for a list of its open windows while the Finder was still trying to get itself organized, and that could bog things down. So grab version 4.1.1 – you’ll be happy you did!