That's kind of a hard question to answer. Each person is a little different.
As for me, I get them all the time. I like them. The majority of sellers that let know they are having a certain type of sale, new items, what have you, are sellers that I have done a lot of business with. I haven't been with eBay very long, but the other sites that I buy from, I get quite a few "updates."
I still get an update from a seller that I wouldn't do business with if she was the only seller in the world. When she sends me her updates, I put in a message that basically says that "You ripped me off once and I'm stupid enough to let you rip me off again." I then add the Case Number of the iffc complaint that was filed! I still get her letters at least once a week. Go figure.
Six inches Lord, that's all I need!