I signed up for it and have been receiving notifications for a few months. I like it a lot; I bought a couple of coats at really good prices, which I wouldn't have found elsewhere.
You decide which stores and which designers you like, and they send you daily e-mails to let you know what's on sale. There are a lot of designer brands as well as mainstream brands like Banana Republic. You can change your preferences any time. You can also stop the e-mails if you're going to be away from the computer, or if you just need a break from all the sale notifications.
I'm not easily tempted by sales, but I do want the best price when I'm shopping for something. So I can easily scan the daily e-mails and ignore anything that doesn't fit into my shopping plan. Right now I have it set to only notify me of accessories and shoes, because I'm shopping for a summer bag and shoes.
Edited to add: You also set your sizes, so that you don't waste your time looking at sales for things only to discover they don't have your size.