@try-alls: I don't beleave that its a problem of mounting other os's, If you feel that the system its slowding down just use the closeall icon it will unmount all the os's, also there are other ways to improving the speed of the device like kernel-power, swaapolube, con900

@deny_winarato: did you install the ubuntu.deb file?

@extendedping: if you are having troubles uncompresing the img on your device I suggest you to do it on your computer, if you use linux you can do it with file-roller, on windows you can download power-archiver.