Added this to Webmasterworld thread, on how much content people add to Adsense sites each day; thread mainly discussed writing.
Early in On Writing Well by William Zinsser, says writing is hard.
The writing I'm best paid for is for magazines; remember when starting out, an editor told me one of his main writers might take a week for 2000-word feature. Also a guy at a news weekly, telling me of being able to bang out 500 words or more in an hour (I think it was) - "Oh, easy," he said.
My writing rate certainly became faster with practice, but still variable; at times may spend quite some time just figuring how to start an article.
Done a handful of features that took up to a month or so, inc research trips - on expenses, happily. But when I don't need to do research, around 1500 words in day seems ok to me. With my sites bringing trickle of money, only occasionally give myself time to add real articles; more often add short forum/blog posts, and photos.