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.
-- Bobby G.