There was a nasty bug in Fedora 17 related to USB devices which I blogged about recently. Rejoice, because your data is safe(r) now. GNOME developers did an outstanding job in fixing this issue. If you try to eject your USB device now, and all the data hasn’t been written to it yet, you’ll see a notification instructing you to wait. After the data operations are finished, you’ll see another notification saying that you can unplug the device now. The device will also disappear from Nautilus side pane.
There are still some less-than-optimal corner cases, e.g. you can click on that notification and hide it, but then it’s not really obvious when you can unplug the device (a second notification will pop up, just wait for it). These issues will hopefully be dealt with in a future GNOME release.