Download Managers are NOT EVIL
Lately I saw a lot of updates regarding download abuse and IP bans. And one of the reason which is rather strongly suggested is because of the use of download managers. And reading your posts, warnings and announcements really gives me the feeling that you condemned using download managers and that they are evil beings. What I would like to say is that they are NOT! Another thing, is that it might not be possible for you to block the use of download managers regardless the kind of efforts that you put into it.
Download Managers are managers! Some of them offers speed boost by multipart downloads but basically they are managers. What do they manage? they manage donwload links and when to execute the downloads. If people can just set up their download managers to 'behave', I dont see the reason for banning people for using download managers. What I mean by 'behave' is for instance, only using one connections for every file and only downloading files one at a time.
Next, why i think you can not actually stop download managers, is because they are essentially internet client. My download manager (and a lot of others) can lie to you that it actually a download manager by saying (when attempting to connect) that it is an Internet Explorer. Now, of course you can detect the number of connections that are coming at the same time, but supposedly that the download managers are set up to be well behave I dont think that there's anything you can do about that.
Moreover regarding the number of connections checking, if for instance someone wants to download bleach and unconciously clicking (maybe right click->open in new window) bleach 1-50 at the same time, they might get banned even if they are not using download managers!
Lastly, what im trying to say is that your fight is NOT with Download Managers and Download Managers are not essentially EVIL. You just have to make them behave. I believe that what you are trying to fight is the excessive bandwidth usage. And because of that, I strongly feels that what you should warn users is not 'Not to use Download Managers' but rather 'Not to use too many connections at once!' and maybe below that (or in the FAQ) you can describe the possible cause of putting too many connections, AND how to resolve them. Please dont hate Download Managers! I have to say that because I often get corrupted zip files when downloading from this site before and using download managers greatly reduce the number of corrupted files downloaded. And it helps you save bandwidths also (because then I dont have to redownload every corrupted files again, right?)