Monthly.
Well, when I'm home anyway. I'm afraid I've missed a few, but managed to make it to my group's recent August tasting, featuring a flight from my favourite region, Jura. None of THAT flight went into the spit cup, I can tell you! In fact I raced out and bought six bottles of each. Such lovely wines!
If you have a chance, go. Wine tastings are fun and informative, especially if they're double blind. There's nothing quite so humbling as not knowing what you're drinking, and nothing quite so exciting as finding out your favourite wine of the night is the $20 bottle, and not the $50 one!