Download File Expert from android market. Its FREE
Run File Expert
Go to App Tab. You may select application you like to backup/save to APK file format. Click [Backup].
All your APK file will be saved to "/mnt/sdcard/backup_apps".
Now you can copy it and give it to your friends that cant download it from android market due to country limitation or back-up it into your PC for future use (You dont have to download it again from the market. Just update it if there are new version)