I recently bought a new and faster Micro SD card for my Epic 4G. I tried to copy the files on my old Micro SD card over through my Windows computer; however Windows Explorer failed. I have a number of applications installed on my SD and Windows was just not happy with .gz format files, etc.
A number of back up and cloning utilities were suggested at various forums; the one that I found be the best, in terms of small footprint and ease of use, is the HDD Raw Copy tool from HDD Guru. It is free, so small and light that you can run it as a portable app, easy to use and did I mention free?
You can try it for yourself from: http://hddguru.com/software/HDD-Raw-Copy-Tool/
If you want to discuss your experience, I have also posted this article at the XDA Developers forum at http://forum.xda-developers.com/showthread.php?t=1376009
There are may other utilities that have fancier interfaces or more functions, but this did the job for me and fits easily on a USB stick.
It is going to be part of my tool kit from here on out. I hope this helps someone.