And what for should they be used? Sometimes, I see that twitter doesn't let me post my links.

I've never used these. What about ow.ly and bit.ly? I hear they work well too.

The matter is that you can type only 4-6 words per line and then it wraps on people's screens. Thus, no more full and long conversations could be possible. On *:INPUT:#:{ enb $1- | halt } is not working for me at all. I'm using EV5 Plugin for http://domyhomeworkonline.net/ and I guess I mixed something in the code editing.