If you're new to the world of San Diego Comic Con badge sales, don't expect everything to go smoothly tomorrow. It rarely does. Last year so many people flooded the servers that the system crashed and Registration Day had to be scheduled several times. The Member ID process should let CCI know exactly how many people to expect tomorrow, so theoretically that shouldn't happen again.
There's usually one element of the registration/hotel reservation process that drives people into rage, and I have a feeling that tomorrow's will be the "number in line" in the upper corner of the screen, which will refresh every 120 seconds. Whether your number is 31, 580 or 7,199, you'll have no idea what it actually means, but it will become the emblem of all your Comic Con hopes and dreams. Perhaps the waiting room will post a percentage of the badges types left, like they did in pre-reg last summer. That would be helpful. If they don't, I'm sure there will be plenty of real-time stats, complaints and comparisons online to use as an estimation tool.
Make sure that if you are traveling with a group, buy your badges together, not separately. Given that probably 150,000 or more people will flood the system at the same time, you could all wind up in radically different places in line, with one of you only able to buy a Sunday badge, another getting a 4-day, another getting a Thursday and a Saturday but not a Friday, and so on.
Remember to have your Member ID info, the Member ID info of the people you're buying badges for (you can buy up to six badges) and your credit card. Make sure your laptop is fully charged, in case of a power failure. And whatever you do, don't refresh.