FWIW, I have taken to going around the house ahead of the Roomba with a
corner brush made of some moulding that has a angled pot brush hot-glued
onto the end. I push all the stuff out from the corners into the center of
the room and then Roomba does the rest. Hopefully, they'll eventually come
out with a cornerbot that does nothing but clean the places the rotary
Roomba can't. Corners are really the Roomba's Achilles' heel and sadly,
it's where a lot of dust and debris like to hang out.
My Roomba was grunting last night, every time it hit an obstacle. I was
laughing so hard I nearly fell over because it really had a sort of human
"uhnnnhhh" quality to the sound. It turns out that a garbage bag twist-tie
had gotten caught in the brush and by the end of the cleaning cycle it had
scoured every bit of paper that covers the thin steel wire at the core of
the bag tie.
It also turns out the dirt detector IS useful. The Red Roomba (which
clearly has a different algorithm than the yellow DirtDog) was on its way
back to the charging base when I dropped some litter on the floor between in
and the base. The "dirt" light came on and the Roomba then began its clean
dance, returning to base after working that area for a few minutes more.