Do you use tempered glass for kitchen cabinet doors? This is for uppers. I'm wondering if it's recommended, mandatory (I'm in CA, USA), or overkill.
I agree with keshlam & it's definitely not overkill. I haven't run into any tempered glass paneled doors for uppers, except my own. Tempered is required for anything within 18" of the floor. And, most cabinet makers will tell you to go get regular glass to put in the empty frame doors they ship.
But, I'd (& have) go for either Tempered or Laminated Glass if possible. Laminated Glass is regular glass glued to a rubber membrane to retain the glass, you're local glass shops may have this to custom cut for same or next day pickup. So, no big shards hurt or kill someone if something happens, like an earthquake.
If it's JUST a glass door -- not set into a wooden frame -- then, yes, I would want tempered glass.
For a framed door, I would use ordinary float glass, what is usually marketed as double diamond -- 3/16" thick, as compared to the 1/8 used for picture frames.
The key for making anything out of glass and wood is to give room for them to move relative to each other. I think the usually allowance is 1/16" per foot of glass. So door with a 24" inset glass would need 1/8" of head room above the glass at the top.
This is little different from leaving slip room in a panelled wood door.
Because a door can be slammed to the detriment of the glass, usually you put put bumpers in the grooves. A continuous chunk of backer rod in the bottom one, and small chunks on the other 3 sides to keep the glass centred.