I don't feel at all that this was a "filler" episode. Way too much good character drama in "What Kate Does" for that.
Like most Lost episodes, I'm just trying to figure out what its real shape and form is. Where it's going. There's certainly a sense that the past five seasons have been well-invested but... invest in what?!
The scene where Dogan was "testing" Sayid evoked genuine groaning. That looked positively hurtful.
Anyone else thing that Claire's blurting out "Aaron" in the other timeline might be some of the "main" universe leaking through? Perhaps a subtle hint at the quantum mechanics at work in Lost?
I'll give this episode a 6.5 out of 10. Not overwhelmingly excellent, but not mediocre either. And who knows: there might be more that we saw in this one than we realize, that'll be more appreciated as the rest of the final season unfolds.