When working off a usb thumb drive or external hard drive, is data or traces of data left on the host pc?

Probably not. More than likely though it will leave a "Most Recently Used" type track that only points to the document. All you have to do is make sure you clean up that type of stuff, if the computer you're on will let you. Again, it will only be a "pointer" type reference, not a copy of the file itself. You can remove all this by cleaning up IE and Windows start menu history (plus maybe some temp files). However, if your'e like me (paranoid), and if you're allowed to install small programs on the computers you're using, check out CCleaner (CrapCleaner). It's tiny and FREE and it makes it very easy to clean up all of that stuff you're worried about. All you have to do after you install it is right-click on the Recycle Bin and then click Run CCleaner and it does the rest. I carry a copy of it around on my thumbdrive.

no,the data will be in your usb drive,but the path will be there.so you can clear it by clearing the history.