I've never used it for business purposes, sure I mention if I'm offering a VA special or something like that but that was not the reason behind joining Twitter. It's always been a personal thing - just for fun type thing.
Oh back to your questions...LOL. I can say that it has been beneficial in driving traffic to my blog and even my VA website.
It doesn't annoy me when people Twitter about breakfast, lunch, dinner, etc. That's the personal level that I like - it makes me feel connected to my friends. Maybe I'm just weird.