I find discussions on Twitter hard to follow at the best of times, even having had a twitter account for years. If you want to have a twitter conversation with a particular person it’s far easier to do it with private messages to that one person. Like you can do here.
The main problem with Twitter is that conversations are not threaded, so what you frequently see on your feed is other people’s responses to THEIR friends, so you often see half of a two way conversation between your friend and a stranger whose replies you can’t see. Also if you reply to one of your friend, and they don’t log in for a while, they can easily miss your response, buried way back in their feed.
My favourite alternative is Plurk, which keeps conversations all threaded in one place and makes it easy to find new responses however old they are. But Plurk is a small community and there’s not much serious conversation going on there.