Yes - How would describe your lack of activity, for example - "I'm sitting around daydreaming of things and um, er, stuff" - It's easier to say "I'm sitting around, thinking about nothing in particular", or even easier is "I'm doing nothing"...
"Something" implies an active role in life or in a situation - While that may not be very descript, it does describe that you are doing "something" - "Nothing" implies that basically "nothing" of an important significance or value is occuring in life or in a situation
Chris