Since I started reading Twitter a few months back, that has been a major worry to me.
Part of my role is to find interesting information and promote it, but it is only part of my attributions.
And of course the more people you follow, the more bandwith it takes you to read all the entries…

I could see some accounts following tens of thousand of people. This is quite a big amount and it’s not reasonable to think that you are read if followed in these conditions. So why follow?

It seems it was a courtesy earlier in Twitter etiquette to follow back if you were followed. But now, users are a bit less hypocritical and tend to follow people they want.
Having said this, you will find many pyramidal schemes on Twitter about artificially growing your audience. Fortunately enough, these are so obvious that is difficult to get caught now.

To get back on the number of channels I could cope with: most of the tweets I find of interest would include a link to validate what is said in the tweet or to develop it. Clicking and opening a new page means that you need to spend even more time for each tweet you read.
As I was building my Twitter network and was (and still am) finding people worth following, I was bound to develop a way to remove the noise (hard sell, or outside my scope) from the information I want/need.

This was the start of the long and painful search for good Twitter tools. I will probably write later on tools as a lot have similar fonctionality with different flavours.
But without any other tool than twitter.com, you cannot be efficient and would struggle to follow more than 50 people, especially if they are productive and generate a tweet per hour!

With some interesting tools, I manage to read hundreds of accounts and I don’t necessarily need to ‘follow’ them (as they may not produce regular tweets of interest).

Therefore, I believe that you may be able to really follow about a hundred Twitter account. And if you do have more, you are doing some kind of screening not to spend your entire day reading tweets.

Of course, I would welcome anyone who would prove me wrong and who, in an hour or two per day, have a way to really ‘follow’ (i.e. read all tweets) more. I would really like to hear how you manage.