There's no need for a exclusively drug dealing guild. But I would like to see "criminal" quests, where you can either help out individual law breakers, or have the skooma trade attached to a separate guild, such as Thieves or Commona Tong.

The Crips and the Bloods are going to make their way into Skyrim, and are going to make sure everybody on the streets has a pocket full of snow, and a pipe full of leaf. Wooord, haha.
I agree though, as I'd imagine a Drug Dealing Guild quests would consist of "Go there > Fetch this > Return", but it would be cool to see a dark and seedy underworld of gangs/guilds that are at war and deal in crimnal acts (i.e. drugs, thievery, murders, gambling etc.,).

I'd love to be a skooma supplier and have a few Thieves' Guild Quests (like the Bal Molagmer quests) specifically about it.

Just so y'all know, Skyrim already has a drug of choice: Rotgut.

It's a whiskey that can only be made in Skyrim and the northern reaches of High Rock and Morrowind (incidentily what the Rumor tab would tell you the Nords had recently conquered - "The Nords of Skyrim and Orcish mercenaries are making war on the Redoran of Morrowind.") And we all know they've moved into High Rock and Hammerfel. Anyone else amazed by that they seem to conquer more land than anyone despite being in an almost constant state of some type of civil war?

At any rate, Rotgut is made in Skyrim due to the concentration of ingredients, and the fact that it needs to be frozen and refrozen in the distilling process. It gets you drunk as a skunk and puts an icey feel in your belly (though whether that's because of its frosty nature or the debilitating effects on your organs is anyone's guess). However, for the damage it does to a person's insides (rotting their guts, get it?) it's been declared illegal by the Empire. So Rotgut is an illegal drug, and it's an illegal drug that many nobles smuggle into Cyrodiil anyone.

I imagine Rotgut being treated like moonshining in Skyrim, with Imperial forces moving into the mountains and hilly forests that have the proper cold and ingredients to distill the stuff and raiding the Moon- Rotgutting cabins to arrest the brewers. Skooma is much too far away to be very popular in Skyrim, and if it is, I call shenanigans. What I want to see is Rotgut, and possibly a warming drug, some sort of smoked herb that makes you feel heated, perhaps increases adrenaline to sustain you in the freezing winter, but also has an addictive effect.

A more fleshed-out crime syndicate of some sort would be nice. There have been attempts at it since Daggerfall, but they have always felt more like petty thieves only. I don't know about a faction specifically about selling drugs...I'm sure Beth will shy away from anything that is going to give them an M rating again.