I recently purchased an Acer Chromebook 11 and things were running fast and great, but then not so much. I tried reducing the number of extensions, but still not so much. Then I read this article (http://goo.gl/Cu4ARs) and here's the trick that worked:
Don't have your files available offline.
Your Chromebook will spend valuable time and resources making sure everything is syncing and up to date. I'm rarely without a connection, so I'm not so concerned about this (and the couple of files that I might need I can individually make available offline on my iPad).
I'm bad for having a lots of tabs open as well. When I move from one tab to another, they reload when they should already be displaying the content. Another trick I've found that seems to help is add extra swamp memory (http://goo.gl/G9QiC). So far, that seems to be helping.
What's your favorite trick?