I found myself skipping most of my lectures (About 60-70% I'd wager). For me, I found the lectures not very helpful since they were just rehashing the material in the notes. I myself found the content of the material easy enough, but the difficulty lay in the quantity of material. All too often I'd just cruise though lecture being like "Uh huh, yeah, I get that. Yep, I get that too. I understand that, yeah". Then after lecture, I'd go home and then be like "WTF, why don't I remember anything about today's material". Sitting though lecture didn't help my memorization of the material, so I ended up skipping lecture.