Spam in email, Linkedin Groups, forums, etc is so prevalent. I see it as part of life on the internet but find it annoying and intrusive. Both legitimate and scam businesses spam. Is it because businesses do make money spamming that it is so wide spread?
Because it's cheap, easy, and requires no imagination at all to do this. Drive-by marketing.
Even then, it's probably not worth the effort - most Internet users tune out, or worse, are turned off, by this kind of thing. I think it's more likely to hurt your reputation than win any business.
This is why the common advice is to spend some time interacting in these groups and communities, and only introduce your content, product, or service when it genuinelly adds value to them. This turns the message on it's head from being something which is 'annoying and intrusive' into something which is potentially 'interesting and useful.'
Your product is useless if nobody knows about it. One way to tell people is to find forums where your target users hang out, and tell them about it directly.
Email notifications sent to existing users can also be important. Your product is designed to solve a specific problem. For example, answers.onstartups.com is a place to ask questions. But after your question is answered, there isn't a pressing any need to continue using it, so you might forget about it.
Sending an email to your customers can be important --
But of course the problem is every other company is doing it too, which leads to a short trip to the spam folder. You can try to justify it to yourself by obscuring the "opt-out" button during sign up but this is scammy in my opinion.
I don't think any good, legitimate business would use spam as a marketing technique, but not all e-mail marketing is spam. Opt-in email lists are quickly becoming popular online marketing tools.
If your use an autoresponder service, customers can sign up to receive e-Newsletters, information about your promotions and your latest product releases. I use aWeber.com for this kind of marketing and I've been very happy with it (although they get expensive when you have lots of people on your list).
Is it spam? Not if the customer requests the email, and not if there's an easy way to opt-out of the list.
This practice becomes spam when customers are signed up without knowing. And an homest business will keep all customer names and email addresses secure, and never sell them or release them to others.