This blog post is mostly just to share a link pasted by a co-worker:
It pays to be aware of the cache, especially when developing games for consoles. In the low-level code avoiding cache misses will be where most of your optimization gains can be realized.
Having your data well structured for systems such as collision and rendering is of utmost importance for keeping things running fast. Just make sure you spend time on the right areas of your code, at the end of the day alot of your code will simply not need to be optimized to this degree if it is coded sensibly.