bits manipulation (C)

I'm an autodidact and I have programmed in C for one year now, but never studied this topic. Apart from operating systems or embedded systems, when do we need to manipulate bits in 21st century ? If you could give some examples...

>>8
I'm aware about the most important changes of C99, someone sent me a recent draft of the normalization. And I know I mustn't use deprecated/bad functions like gets() or tmpnam().If you have suggestions about an up-to-date/better book, you're welcome.

>>9
Ha ha, ok I'll do it. First, I was thinking about taking a look at imagemagick but I will look at mplayer, thank you for your advicce.