What are the best loyalty programs you've used or heard of?

The only one I've ever really used (other than credit card points for travel and $$$) was Dropbox, because it made a ton of sense to do a bit of work for a lot of extra storage. That was years ago though and generally I won't participate in them because the reward isn't worth the social capital I spend.

The only way to get me to talk about something with my friends is if I love it and think they will also love it. Then I'll do it for free and a loyalty program probably would be a barrier, not an encouragement.

Standard chartered credit card (not a loyalty actually) because of direct cashbacks and points that you convert to Amazon vouchers

birchbox does a great one

https://loyalty.linkcard.app/es/ Linkcard allows to create your loyalty on the spot, without plastic cards or whatever.