I remember the games I ran back in the early 80's - low on details, high on dungeons. Cleric's worshiped some unnamed force until I bought the Greyhawk folio, and even then it just was a name filling a caption on the character sheet.
After seeing the detail given in Dragon Magazine to the racial and Greyhawk deities, I tried my hand at designing my own deities (notice I don't mention Deities & Demigods, as it always seemed more like a high level monster book it my eyes.) Although I want to say they were well designed, I can't find the notebook that contained them, and I suspect they were pretty crappy. Still, I used them in my own home grown campaigns, which always seemed to take up more time preparing the background for than was ever used in game.
Now, I've swung back the other way, where deity details are glossed over in my campaigns. One of the nice things about the limited sandbox of Tenkar's Landing is I can probably get away with detailing just 2 or 3 deities to begin with without worrying about whole pantheons.
How important are deities in the campaigns you run and / or play in?