A more recent version of scripts may be available at scripts.irssi.org.
This script combines multiple lines from the same person into one line. This can safe a lot of space if someone talks in many short lines after eachother. The lines will still be normal in your logfiles.
It's still quite beta, but it seems to work. But every time it combines lines, it must redraw the whole screen (remove the redraw line from the script to see what happens otherwise :p). I can't work around this without breaking logfiles.
This script is best explained with an example. Without the script you would have
01:23 <foo> hi 01:23 <foo> i'm back 01:24 <foo> anyone awake? 01:24 <bar> hi foo 01:24 <bar> what's up?
With this script loaded, you get:
01:23 <foo> hi | i'm back | anyone awake? 01:24 <bar> hi foo | what's up?