When does a MySQL DB slow down?(some figures might help me understand easily)

Is it bad to normalize data cause it takes more queries to get the same data??

I have been learning PHP and MySQL from 7 months(Not a very long time).I want to become a Professional , So what should be my approach ?

Designed a clone of IMDB using Codeigniter. http://imdb.techmax.co.in .

Last question is not related to this section but it would be great if you answer that too.

Peace.....