When should they not? Your description is lacking.

Doesnt seem to work

Well, it does what it says.

This messes up the Myspace profile editor. The page;
http://profileedit.myspace.com/*
should be added by default to the excluded pages to prevent this.

Hiding instead of completely blocking is a limitation of Greasemonkey, not this script. If you want the ads to be blocked completely, try using Adblock or the Proxomitron.

What does this script do exactly.

I don't think
http://www.sacracorona.nl/
is Shoutwire.

I like the script that Mike Hicks posted better.

Youtube is owned by google. Might as well look like Google too.

Pretty good. The download icon is so well blended you would never know it wasent originally there.