The total cost in file size would be something like .1k for carriage returns unless you have a super long stylesheet.

I personally use the long method:

.someclass { font-family: verdana; font-size: .8em; etc...}

I hate having long pages of code. When doing a stylesheet like you all mentioned it can take up 50-150 lines of code. I find it much cleaner to put it on one line. I do sometimes break it out if I need to read it, but then I simply put it back where it goes. Besides, if you've got a text editor that offers syntax highlighting for CSS, then it's not problem at all.