electricandroid posted this and it is very useful so I will repost it here:
There is a reasonably quick way to find your friends on Journalfen, Greatestjournal, and Insanejournal.
- Copy/paste your flist from your LJ user page into Word
- Do edit/replace of the commas with ^pfriend add so the list ends up looking like this:
friend add icarusancalion
friend add amothea
friend add ...
- Copy/paste this list into the admin/console
-Then to find those who didn't turn up, save the resulting HTML file (use View / Source and save that) which will give you a list of all those you need to hunt for
-Check the people you've friended to make sure they're the same ones. Most people are using the same names, but sometimes names are taken. For example, the ncp on greatestjournal is not the same one as LJ.
IJ can't cope with really large flists - so do it in parts.