Reb Tzadok Hakohen in Pri Tzakik in his 4th ma'amar on Shabbos talks about the differences between the kedusha of the different parts of Shabbos. He says about Friday nights that it's the time of "Chakal Tapuchin Kadishin," "the field of the holy apples." A field is outside. And Friday night is the time to go out, to be active, to stay up late doing holy things. As opposed to Shabbos day which is a more passive time, a time to take a nap, etc.
But during the week we need to get up early for minyan or to learn before davening before going to work. It's the time to go to bed early.
But the yetzer hara's a funny thing. During the 6 nights of the week, people have a yetzer hara to stay up. They need to do things with the family, surf the internet, read the blogs, etc. And for tovim shebanu, to learn. It's common for many people to stay up till 11:30, 12, or later at night. So the yetzer hara wants people to stay up late during the week, because it shters their ability to start off their next day the right way but getting up early for holy things.
But Friday night when there's an inyan to stay up late, to learn, to go out to a tish, etc, we can barely get ourselves to stay up 30 minutes after the end of the seuda! People who can't manage to get themselves to bed before 11:30 during the week can't stay up pask 8 PM during the winter! It's so meshunadik. It just shows that it's atzas yetzer hara.
But at least if we're in touch with that, we can start planning how to outsmart that nature, to do the right thing during the week, and on Shabbos.
BTW, there's a nice Nesivos Shalom on parshas Shmos that quotes the Me'or Einayim that I talked about here, and expands on it.