I have been using Twitter for ages now (a good few years) and I have never got around to sorting out my lists until recently because of time. I would imagine that many others are in a similar boat, only because when I tweeted about lists, a few others asked for more clarification, so here it is.
Lists are a feature where you can group certain users together. I could have lots of lists but I tend to just have a few. I have one for people in Hampshire so that I can see what local teachers are tweeting about and I have another for people I talk to or follow regularly. These are the tweets that I now look at in more detail. Before I found that I was spending ages looking at Twitter but it didn’t feel productive. Now my time has been reduced but I feel that I am getting a bit more out of it. I know that there is the chance I’ll miss something from someone, but as @dughall says, it’ll get retweeted if it’s useful. I do scroll through the main timeline now and again, but not as regularly as I used to.
I would definitely recommend spending a few hours going through the people you follow and organising them into lists. I found the best way to set this up was through the Twitter.com website. I simply scrolled through the people I was following and I added some to lists. It only loads 10-20 at a time so there is a lot of scrolling, but you’ll get there in the end.
It may seem like a big time spend at the start, but it will make you feel much better afterwards.