CrossFit has espoused a fitness system that is observable, measurable and repeatable. But, like any system that uses an empirical measurement, it is only as effective as the data recorded. When it comes to you and your fitness goals that means the best way to gauge progress is by looking at the details of your workouts in your training journal.
We've been using Sugar WOD for a couple of months now (you're signed up right?) and everyone seems to like the ease of use and the ability to "Fist Bump" as well as comment on your fellow 30A CrossFit athletes' performances. By tracking the weights you use and your times on the benchmark, it's easy to see your fitness increases over time. And by looking at longterm trends you can see what workout strategies work for you so that you can accelerate your progress.
As noted in this CrossFit Journal article: "It’s satisfying to see improvement, and keeping track of data can also tell athletes and coaches what’s working and what’s not, allowing them to make appropriate adjustments."
One of the best features of Sugar WOD is the note section. You can add details on anything pertinent to your workout performance such as sleep quality, stress levels, how you mentally approached the workout (see my example above). These are details that will really help you develop as an athlete.
I've used this feature more as I've recovered from a hip injury. By noting where I felt weakness during the workout, I can make better decisions on a mobility and recovery strategy.
You don't need to write a book after every workout but you should be noting factors beyond your times, weights and whether you "went R'x." Check out this post for more ideas on what you should be taking note of in your journal.