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.
Kparal's Fedora Blog 
THANK YOU!
I’m glad this got fixed before the final.
We need to spread this information so that folks know how it works. /me goes to tweet/dent etc.
I have two computers with Xfce/Nautilus. On notebook, I always get warning and device is not unmouted. But on the second computer, Nautilus always unmout even copying in progress…
Please report a bug into https://bugzilla.redhat.com/ . Without lots of additional information no one can really tell where the difference is.
Why is it that the progress bar goes to the end fast when you copying data onto a usb-drive (you would think it’s done), but in reality it takes an other few minutes till the data is copied and this time the progress bar has long gone….? So no real indicator of the copying progress, unless your usb has light-flash that is indicating the working progress.
Yes, that’s a bug that Nautilus developers should fix in the first place. The reason is that there is some internal buffering that speeds up usual operations. But in important places like this the applications should reflect the real state of copy operations, not the buffered state.