Y’know, I’ve never seen an actual d100. First time I heard about it, or read about it possibly, I was convinced my leg was being yanked.
All I could picture was this hyper-thyroidal, bowling ball sized thing that would, in fact, never stop rolling.
Guess I wasn’t too far off, after all.
[sub]FWIW, we always used two differently colored d10s for that, with the 10’s die always one specific color, established beforehand.[/sub]
Yeah, I’ve seen a d100. I think it was about the size of a golf ball, and it never seemed to stop rolling. What’s more, when it DID stop, you had to lean over the darned thing to try to read it…and if you breathed heavily, it would roll again. D30s were almost as useless.
However, having a d30 gave me a sense of COMPLETENESS in regards to my dice collection.
To complete the “Dice Highjack”
Just what is a d30 used for? I don’t recall ever seeing a game system that called for it.
I had a d100 and a d30. The d30 was a perfectly functional die, it just didn’t have a function. It was made solely because helpless dice collectors like me and Lynn would shell out two bucks for one.
The d100 sucked. I gave it to my cat. They’re still making them, this time with easier to read numbers. Damn things still won’t stop rolling, though.
Anyone seen those gigantic d20s they have now? The ones that are the size of your fist, and cost about twelve bucks? I want one.
Badly.
I remember some “Random Effect” tables that called for a d30. I think they were published in The Dragon sometime in the mid-80’s-- Probably to help gamers justify owning such a useless die. 
Miller, that sounds so cool, can they be found online?
That would make a natural 20 much more dramatic, I’d think.
And actually, now that I think about it, I want one too, just to have something to brandish at the monitor when the PC-RPG of the week seems to be cheating. Again.
We had two separate AD&D campaigns for this purpose; we’d assess everyone’s mood when we got together, then pick which campaign to play in. There was the high-level, serious, “My character single-handedly invades the Lands of Iuz” Greyhawk campaign. Then there was the low-level Forgotten Realms campaign, with Ahnold of the Elven Vood (an elf who lifted weights with his ears), Misfirin Dendrite the psionicist, a masochistic evangelical priest of Ilmater who kept broken glass in his pocket to play with, and two thieves who couldn’t successfully steal from anyone except each other.
I haven’t gotten my hands on a d30 or d100 yet but I am the proud owner of the exceptionally useless d16. (picture a d10 with 3 more facets on each half.)
The ONLY use I’ve come up with for it so far is to track score in highlander the card game (you start with 16 or 15 and go down to 0, rarely getting above 16)