I've watched BtVS all the way through once, and then again up the end of S5, all marathon-style on DVD.
But I have some issues with the last two seasons, and consequently my rewatching of these has been much slower and more haphazard. I rewatched S6 from "Entropy" to the season finale a few weeks ago, and then went straight on to the first three eps. of S7 (partly because "Same Time, Same Place" is one of my very favorite Buffy episodes). Then I watched "Bargaining," and then I stopped for a while.
Then back to S7 for a few eps, then back to S6 up to & including "Life Serial" (which is another particular favorite, and one of only 2 S6 episodes I've seen more than twice). Then, today, back to S7: I had the day off & I watched a preposterous number of episodes while folding laundry.
And watching "Never Leave Me," seeing Buffy and Spike interact... here it is... it dawned on me, "Yeah, I actually ship that."
( This whole time I've been kind of anti-spuffy... )