On our last trip (May '08), we had 10 different ADR's for dinner. We showed up early to at least 8 of them. (We just happened to be in that particular area at that time...we didn't plan on doing it that way).
At every one except LTT, we were seated early (anywhere from 10-40mins). One of the meals we were seated early for happened to be CM. Our ressie was for 7:30. We showed up at 6:30 (DS loves the CR and we planned on doing a little shopping there, anyway) and we were seated at 7.
BTW, we were out of there before 8, so 6:30 should be early enough if you aren't able to be seated earlier.