experience with tags schemas

Greetings,

Does anyone here have any experience with tags schemas on postgresql ?

I am struggling with a schema inspired by "scuttle" described here :

http://www.pui.ch/phred/archives/2005/04/tags-database-schemas.html

Performances drop dramatically when the data set increases. Is it
"normal" and I should look at other data structures ? Or am I doing
something wrong ?

If you need more information, I'll be happy to give it to you.