"I may be love's bitch, but at least I'm man enough to admit it."
I'm certain it wasn't intentional, but the seeds for two of the major plot arcs of Season 6 are planted right here, in episode 8 of Season 3.
The first arc that's birthed here is Willow's abuse of magic. Hello Dark Willow! Her trying to use a spell to stop the lusty feelings between she and Xander is the first time she attempts to use magic to solve her personal problems. It's a small step from changing Xander's feelings to wiping Tara's memory. Her motives here, of breeding discontent between lovers, runs parallel to Spike's motives of winning his lover back. But in the end Spike realizes there are better, more reliable ways of achieving his goal, a realization that Willow doesn't seem to come to. Indeed, you can imagine her thinking that if Spike hadn't interrupted them, maybe she could have convinced Xander to go along with it and Oz and Cordy never would have caught them together, Cordelia wouldn't have been wounded, Oz would never have (temporarily) broken up with her.
The other arc that arguably begins here is the Buffy/Spike friendship (though you could also argue that relationship began in Becoming pt.II,), and here I'm talking more about their relationship from Afterlife through All The Way than about their relationship post-OMWF. There's a bit of a sexual charge in their interactions here (particularly when she has him pinned down in the kitchen), but more than that is the tolerant amusement with which they seem to regard one another. Buffy threatens several times throughout the episode to kill Spike, but she never seems particularly serious about it, and in the end she lets him go without a fight. They can see right through each other - she knows right away where he's keeping Willow and Xander hostage, and he understands her feelings for Angel better than any of her friends do (her admission that "I can't fool myself. Or Spike for some reason" is possibly my favorite line in this episode). They banter and quip at each other throughout the episode, while Angel remains mostly stolidly quiet. And of course they (and Angel too) get to fight together, the three of them taking on a much larger contingent of vampires and winning.
Lots of good scenes in this episode, particularly Spike threatening Willow with the broken bottle, then crying on her shoulder, then changing moods suddenly and threatening her sexually (yowza!). Then there's Spike confiding in Joyce while drinking hot cocoa, which has become a fanfic cliche, but the scene itself is still pretty damn adorable. Cordelia getting impaled on the rebar is still disturbing. I also love that Buffy did so well on her SATs, because she's bright and articulate and has excellent instincts, so it makes sense that she would do well in a high pressure testing situation.
The script, by the way, is filled with great directions:
Where Angel registers only a split second of disbelief before he reacts, growling and flying through the door, except OOPS, he can't, and he smacks into the invisible barrier with all the force of a really talented mime.
Xander rises behind him, fury etched on his face -- and Spike swings the microscope behind him, etches that on Xander's face instead.
There is silence. Buffy and Angel are comeback deficient.
Buffy is caught between the other two, by the sliding ladder in the middle of the store. Ladder-fu ensues.
They come at [Spike], and he moves like lightning. He fucks them up.
Somber music from some band of young hipsters (or perhaps a stunning Lilith Fair chanteuse) plays on the soundtrack as we see Angel, standing in silent grief.