Stuff.
The opposite can also happen. If I may pimp my own video on here (http://www.youtube.com/watch?v=5YQffnEho-I), a good example is what transpires at 2:52 with the use of です, changing it to デス(カ). It all makes it appear more rough/masculine in a way.
There's all sorts of ways hiragana and katakana are used so don't be too alarmed when you see something like that.