How they've grown...
The folks over at With Character have a bunch of essays looking at how some of the scoobies handle themselves through each season. Some interesting reading, with varying levels of insight from the different authors. Most focus on the early seasons, but some (Like the Xander essay by Bastardsnow) go as far as season five.
"... Buffy ends the season much as she started it. A little older, yes. A little wiser, I’m not so sure. Instead of learning from the fallout of keeping secrets and talking to her friends and family, she leaves them behind again, shutting them out of her life. "
