Just received the D800 in the mail today. Overall it feels better in my hands then the 5D does. Build quality is just phenomenal, the knobs and switches all seem like they're much stronger than on the 5D.
Congrats on your new camera. In my experience, the D800 can be used in sports application with lower burst rate as already identified. Your success rate will vary based on your experience, technique, AF and SS settings that you use.