Just wondering, has anyone played around with the addiction option for items in the Creation Kit?

Does it actually work, or is it a relic from Fallout 3 that doesn't do anything?

AFAIK, it's non-functioning in Skyrim (it is a Fallout thingy) - http://www.creationkit.com/Potion

Although addiction/dependencies on health/magicka/fatigue potions is an interesting idea for a mod...
Now that's a decent idea for a first mod I'd like to try.

I might play with it a bit tomorrow, but something tells me the actual addiction property is entirely disabled.

It is disabled.

You can write your own ... sort of ... I have for a Quest (I just use a repeatable sub-quest with two stages ... 1 is addicted, 0 is not addicted ... to one particular potion ... so it persists across saves ... just check with OnUpdate on player every X game hours ... kinda). Works OK (ish).