[this is an expansion of my tweet earlier today.]
Getting the email address of your users and keeping in touch with them is a classic technique. So classic that it's been mentioned in umpteen different places - I won't even bother to find the references. So classic that quite a lot of companies do pick it up, eventually.
However, there is one detail. The emails that you send need to be wanted by the user. This is a detail that escapes frequently. As a result, I am getting a lot of updates from various companies "hey, we are doing this!" or "please take a look at our new new model of humbambillistic hyperbanana!" - while, if they noticed, I did not really use their service. I tried and did not find it too compelling, or it did not solve my problem.
More impulsive of you will exclaim - "hey but unwanted email is precisely the definition of spam!"
Well, not quite. The thing is, I might have agreed to be mailed at a particular point in time. When I thought this source might be interesting. However, the first mails proved not as much substance as I wanted. Should I unsubscribe ? Maybe. However, sometimes with the subcontractors acting on behalf of representatives of the newly formed subsidirary of the ... well, you get the point. It might not be trivial.
On the other hand, I do not want to send this straight away to GMail's "spam" folder - because it will harm the users who maybe are interested.
So, I found a way that would not harm anyone and requires minimal involvement from my side - simply create filters and transit those "not interesting anymore" messages to a special folder to settle.
Maybe I read it one day when I don't have anything to do, maybe I won't. But I won't read them now.
I do this if I consciously remember that I get more than two messages with the first three sentences not holding the content that is informative and useful for me.
This reveals the other side of the coin - it's somewhat ok to poke me if I do not remember when was the last time you poked me. Unless the background pokes from different places burst together such that I get sufficiently annoyed with random flood of poke-like messages on a particular day.
I wonder if I am unique in seeing this problem (and this maybe just my own laziness), or there is indeed something to it.