I DO send auto-DMs (using TweetLater), but if you read the comments there and view the results of the poll, you'll see that I'm very much in the minority; it seems most people really dislike it. I left a (rather long) comment to balance things out a bit. Here's an extract:
Have I ever received an auto-DM which provided value to me? Absolutely! ... The best example being when I followed a guy in Australia. He’d caught my attention, I followed, and his subsequent auto-DM resulted in a couple of ‘learnings’, a potential JV partner and a blog post.
I guess with all things in life, you can’t please all the people all the time. And nor do I want to. I want to build relationships with people I like and respect. The feeling isn’t always going to be mutual and hooray for that - keeps the world interesting. :o)"
So - that's my view. But you should be aware that it will really upset some people, so if you are going to use TweetLater to send automated direct messages in Twitter, then spend a little time thinking about what your objective is and word it/them accordingly. I'd better go off and reword mine... [shuffles off]