To put it mildly, I'm less than enthusiastic about Google Reader's new (Oh Gawd, 20pt line spacing) interface. Is there an extension for Chrome which can put it back the way it was, at least in terms of line spacing and "useful reading area"?
Ditto! Don't know why Google loves all those whitespace.
As for your question, here is an extension for Chrome: FIxStyleSheeet For GoogleReader, or if you want a userscript, check out Google Reader compact. I am using the userscript since it does the same as the extension minus the memory usage.