We are not sure what type of tree the etz hada'as was. The Tanaim had four different traditions on the matter: wheat (which at that time grew on a tree), esrog, fig, or grape. The practice of the Vilna Gaon was not to eat grapes on Rosh Hashana, following the opinion that: the etz hada'as was a grape vine, and that Adam Ha'rishon was created on Rosh Hashana (which that year was on a Friday; according to the calendar system we follow today, lo ad"u rosh, we see to it that Rosh Hashana never falls out on a Friday), and, according to the medrash, the same day he was commanded by Hakadosh Baruch Hu not to eat from the etz hada'as he violated that mitzvah. Therefore, because we don't want to repeat Adam's mistake, we avoid eating any grapes at all on Rosh Hashana, even thought our grapes are clearly not from that etz hada'as.
The tradition that the etz hada'as was a grape vine additionally includes a comment that much tragedy, pain, and suffering have come about over the years because of the grape vine. People get drunk from wine, loose their senses, and act out in a most irresponsible fashion.
Some mekubalim suggest that perhaps the takonas chachomim to recite Kiddush on Friday night was instituted to serve as a tikkun for the sin of the etz hada'as. Since Adam Ha'Rishon sinned on erev Shabbos using grapes, we use the grape vine on leil Shabbos to show how one can act in a most responsible and most proper way by b'dafka using that wine which often has led men to sin or otherwise act improperly.
The medrash points out that in the beginning of the parsha, Noach starts out as an "ish tzaddik tamim", but later on turns into an "ish ha'adama", and he defiled himself ("vayacheil Noach", he made himself chulin) by getting drunk, losing his senses, and acting in a highly improper fashion.
We congratulate those rabbonim who have not permitted use of liquor in their shuls. It has recently become a new "shtik" that yeshiva bochurim drink liquor at weddings or at a kiddush. This is a most improper practice, and the parents or rabbonim of these young men should see to it that they discontinue this "minhag shtus."
In the beginning of parshas Vayetze we read about Yaakov Avinu running away from Esav and dreaming of a ladder extending from Earth to the heavens, and angels ascending and descending the ladder. The midrash has several interpretations of this dream. One interpretation which appears in the gemara Chulin assumes that it is the same group of angles who ascended to heaven, saw the image of Yaakov Avinu engraved on the kisei hakavod, and later descended to see if in real life Yaakov Avinu actually lived up to the potential he had (according to the demus dyukno which they saw on the kisei hakavod.) When they came back down to Earth and found Yaakov fast asleep, bikshu l'horgo - they planned to put him to death. From the entire beriah, man is the only creature that was endowed with sechel, and therefore the angels were thought Yaakov was guilty of a serious sin - how can such a creature waste his time by sleeping? He ought to use all of his time to accomplish great things! The Torah continues to tell us, "v'hinei Hashem nitzav alav", that Hashem hovered over Yaakov to protect him from the angles. Hashem understood that while it is true that one who was endowed with tremendous potential ought not to waste his time by sleeping too much, every human being needs a certain amount of sleep to maintain his good health. Human beings have tremendous potential due to their unique tzelem Elokim and should not waste that potential of chochmo and sechel by drinking or by oversleeping. To preserve our tzelem Elokim we were commanded v'holachto b'drachav, to go in the ways of Hashem - ma hu, afa ata... Hashem is original, creative, artistic, etc., we all possess this tzelem Elokim and therefore ought to act in a creative, artistic fashion. Sitting around and aimlessly day-dreaming, i.e. being guilty of bitul zman, is considered a serious aveira, since it is an outright violation of the mitzvah of v'holachto b'drachav.