Well, I've not really had any success with twitter. But, at least with a tweet and about two retweets from others we get like 40 hits at a go but it's short term. However, I think the key to success on twitter is if you have a very active twitter account with good amount of followers. Then, you can easily convert followers and also get a substantial traffic from there.
Although, natural tweets of your pages are the best, that is, others tweet them on their own accord. But, it's sad that it is almost limited to the big names alone.