I am one of the ISO testers at Mint and I am running LMDE full time on my main machine and it has been running great. It is nice not having any of the upstream issues from Ubuntu. I still like Ubuntu and the Other Distro's based off of it but Debian is very stable even the testing version of it. I think Pinguy could do a version of Debian testing and it would be great. 
When I was a noob, I would have been stuck in my tracks at the partitioning section. Is there a reason Ubiquity can't be adapted to it?
If PinguyOS got even faster under Debian Testing, I'd use it in a heart beat. 
Well I am not the Dev but they decided to write a installer from scratch, they did not use Debian's installer due to it not being as user friendly. As to not using Ubiquity I would think it would be more of a pain to port it to Debian that write there own from scratch.