I am of the mindset to always upgrade my theme and plugins when a new version is available. I rationalize this by believing that if everything is of the most recent version the pieces are most likely to work together seamlessly. In so doing, I tripped myself up.
I use Google Analytics to track this website. To do so involves pasting a snippet of code into the header of each page that enables Google to peek under the hood if you will. In updating the site I reinstalled my header file and therefore deleted the Google code. For the past few days my site traffic looks to have flatlined, while I know that this is not so.
Another side effect is that I had changed the font color from the stock grey to a darker color to make this blog easier to read. Alas this change got lost as well. Luckily I remember that I wrote up how to change this so all I have to do is go through my article archive and follow the instructions.
So remember: if you update your theme you may lose modifications that you made to your site. Probably not terminal to the health of your site, but definitely a bit annoying.