Why would my dimmer switch only dim lights about halfway?
Most new dimmers rated for CFL/LED use have an adjustable low-point setting. Check and see where yours is set. 

Refer to the "Dimming Range Adjustment" section of the instructions here: http://www.homedepot.com/catalog/pdfImages/cb/cb27dfa7-40a6-4788-9112-c2a619a4b2e0.pdf