Everyone has different experiences, but don't be surprised if, a few days into preconditioning, you feel pretty crummy. I was miserable in preconditioning because I went into a carb withdrawal. My sister felt bad during her preconditioning because she was going through caffeine withdrawal.
Bleh. It all depends on how dependent you were on the things we can't have while on the plan.
Also, you'll likely see a decent weight drop at the end of preconditioning, as well as the first couple weeks of the plan. DOn't freak out or become discouraged, though, if you stall out after losing about 12-16lbs (about 4-6 weeks in). That's a totally normal plateau that we all seemed to hit right around that time. It won't last long, and it's necessary for your body to kind of go into "shock" at that point and get used to the weight loss and diet change. Like I said, it doesn't last long (maybe a week?), and is just a phase--though it's easy to get discouraged during that time.
Otherwise, try to stick to the plan as close to 100% as you can, and you'll be amazed at the progress you make. The plan absolutely works, but you have to work the plan in order to make that happen.
Good luck, and definitely let us know if you have any questions, hit any rough patches, or are ever feeling kind of down. This board is a great support network, and I never could have done it without these ladies!