I've just published my guide to
Mixology in Late Night. It was a really rough guide to write. Mixology is certainly not meant to be a big money maker, but is more of a party or utility skill that can help single Sims, or families alike. The drink effects are quite cool and should be pretty powerful in combination with traits, and lifetime rewards. The skill also helps a Sim to raise their Celebrity level, which is an important metric in Late Night.
Of course this will be revised, but I'd rather get it out to the community in an imperfect state rather than delay its release. You'll notice I'm missing the drinks served at the 'Aquarius', which may be named something different. I just happened to pick my own Zodiac sign for my Mixologist. It could be pure coincidence. This and other things I could use help improving. Also, like TommyT I had a really hard time making anything substantial money-wise. It's actually quite frustrating watching Sims order food or get jammed up waiting at the bar.
I fail to see why more Sims aren't ordering a drink when my Sim is a Celebrity. I'd totally order a tall drink from a star, if only to meet them.