Personalized Recommendations at Etsy

Very interesting article with some cool approaches. I'd be really interested to know how often the model needs to be trained? Seems like a lot of purchases are holiday/seasonally relevant and you'd hate to be suggesting valentine's day gifts on Feb 20th because everybody was buying them 2 weeks ago. Also be great to see any insights on how many features you need to get a good guess on a users tastes and preferences? Are 20 numbers enough to represent most of the dimensionality of Etsy products or 100 or 1000?

Fantastic! I had been looking for this kind of overview of basic recommendation systems for the past few months, and this is the first time I've seen so much understandable yet really helpful information in one place. If anyone else knows of similar kinds of articles, I'd appreciate suggestions.