i have learned that lectures (for me at least) are only occasionaly helpful. sometimes the profs suck, or more likely, i am usually not prepared to learn what they are teaching. if i haven't read what is being presented it is way beyond me to get anything out of it. my advice is to spend the time learning the way you learn best. for me, that is late in the term under pressure, on my own. not very effecien, but old habits die hard.
one thing that i consider is face time. it is pretty important here, as the lecturer is typically the dept head, who is our oral examiner. since our entire grade is based only on one oral exam, i try not to miss ALL the lectures. usually early i miss a bunch and then toward the end of the year i titrate upward, so it appears as though i am a dilligent student!