Everything you need to know about using Twitter for marketing and PR is at this very descriptive url:
That’s right: Don’t. Don’t use Twitter for marketing.
Let me draw a comparison for you: What would you call someone who uses a program to automatically send you an annoying volume of email? A spammer. So what makes you think that because it’s 140 characters and on some trendy web service that blasting away with soulless and automatic links isn’t spam?
So that’s why I say automated means to add content ...