Nautilus file copy progress is often misleading
Due to aggressive I/O caching, file copy progress indicators are often much different from the real progress especially when copying to slow (USB 2.0) devices from devices with much RAM. Copying a heavy (1-2GB file) to an USB2 (or even 3) device results in the progress being displayed very near 100 within 1 second or so, and only being updated to 100% in minutes, giving an idea of being stuck and irresponsive. Even worse when it's cancelled and re-attempted, as the previous copy operation is still running in Nautilus in background. Using a more advanced approach to file transfer operations would give real progress and avoid confusion.