No, I never used "Tablet PC" when talking about Tablets like the iPad, Android, and Windows tablets.
I'm too used to the look of a Desktop PC being a large powerful PC tower, or rectangle shaped computer, so it sounds kind of weird to say "Tablet PC" because a tablet is a small handheld device like a calculator or phone.
I notice a lot of subtitles for Korean videos use the term "Tablet PC" instead of Tablet. I guest, people who subtitle foreign videos recorded in Korean like being more detailed when talking about tablets instead of saying iPad, Tablet, Tab, etc, or Korean actually say Tablet PC instead of Tablet like North America where most people just say tablet, iPad, or tab.
In the past, older Windows XP touchscreen laptops which folded into a tablet were called Tablet PC. But, these Windows XP tablets were actually laptop PCs with Windows XP Desktop PC OS.
Well, I wouldn't use tablet pc when I am talking about tablets....
They are not that similar to PC's...if anything... I believe they are very similar to phones.
I feel using Tablet PC can be useful for talking about a Microsoft Windows tablet because some people think PC means a computer running a Microsoft Windows computer/PC. But, most people think of a Apple computer as a Mac/Macintosh computer or Macbook for Apple laptops.