In my opinion Twitter is one of the best Social Networks for advertising and promoting products. Usually I was only concentrating on Google Plus, until I started trying out Twitter. I have been getting about 25% more visitors since then. What about you?
I would not say that Twitter is the absolute, "be all end all", best social network for advertisement, but I will say that it very well has the potential to be depending on how much effort you are willing to put into it to tweet useful things and build your followers. Think of it as a miniature marketing firm, where you tweet something and then, say, out of a total follower base of 5000, 350 retweet your tweet. Many of your followers can have hundreds to thousands of followers of their own, and when they see this retweet and find it useful, a small percentage may choose to retweet it again, so on, so forth. Do you see how this can have the potential to make you very rich very quickly? This is what I mean.
It obviously pays to have more followers, but what you want are targeted followers who are more likely to convert, who are more likely to purchase or complete an offer for you. This is where the money will begin to roll in. I have seperate accounts for each niche I dabble in (finance, dating, health, gaming, SEO, etc.) and I send very specific offers to my followers in each one. Needless to say, I rarely get a low conversion rate even with only a few hundred followers.