We all make mistakes. Heck I've been doing this for 8 years and I still kick myself for doing certain things.

Most common mistake is what I said above.

Most novices are usually 4-8 seconds behind the fastest car in the class, but that's a rough estimate based on my instructor experience. Some are quicker and some are not. Just like any sport you have people who are extremely well adapted to a sport while others need practice.