I was pretty active on Twitter a few years ago; I did find it to be a colossal waste of time. The feed zooms by so fast with the millions of people posting everything from political opinions to what they had for lunch...any promotions you're trying to have noticed just get lost in the shuffle.
That is, unless you live a life of leisure, and have the time to sit there re-posting every 10 minutes...oh, and don't forget the time to actually exchange tweets with folks, and re-tweet others' posts...it's a social media, after all, and if you don't show interest in others, and help them promote their stuff, too, you're going to be very disappointed in the results. (Or rather, lack thereof.)
Since I am not independently wealthy, and have to do my own household chores, I don't have that kind of time, so I gave it up as a bad job. Once in a blue moon I'll post or re-tweet something that I see pop up on Facebook or in the news that I feel is worthy of notice...otherwise, I don't bother with it.