When the applet is on a vertical panel, its horizontal size is limited, and the speedLabel clashes with the name label. I fixed that by moving the speed values below the sensor name in this case.
I also added some cleanups unintentionally (the first three hunks), as I couldn't find a way to change the diff after it's submitted. They remove an unneeded import, and fix some uninitialized variable warnings. Feel free to ignore them.