If you have the cable and not a Mac user, you can create an account on the MiniMed Carelink website and upload your readings there. They have some neat graphs to help with trending analysis.
There are also other options:
If you have a Smart Phone, there are apps that also keep track of all that stuff, Glucose, Carbs, Insulin, Exercise, etc. They have some tracking options for trending.
As the others have said, its only as good as you make it. YDMV