We were there during "Jersey week" in November 2004, from like Oct 30-Nov. 6.
The crowds were not as heavy as they were the previous year when we visited mid-October, over that federal holiday weekend, Oct 12-19, 2003.
However, there were definitely a high percentage of folks from NJ, that became apparent. When people talk about large crowds at that point, I think they are referring to the difference between that and other parts of November. Still, we rarely had to deal with wait times longer than 20-25 minutes if I recall. And by getting to the Parks early, at opening time, and taking advantage of Fast Passes, you can avoid most of those lines.
The other factor that is a negative that time of year, is the park hours are not extended. We also visited in June 2005, 5-12, and I'm sure there must have been more people there at that point. But because the parks were open til 11 or 12 nightly MK, 9 MGM, 6 AK, etc. it seemed like the crowds were more spread out, and there was more staff on duty, so it didn't seem as crowded.
Still, all in all, I think you'll be fine during Jersey week. Just go with a plan, and make your advanced dining reservations early, so you don't get shut out of anything you want to do in that fashion. But I do remember making adjustments to our dining reservations while we were there that week.
Good Luck, have a great time.