Installing Lion with duplicated installer I see many people asking how to save the Lion installer, and ofter the way to go is unpacking the installer and saving the disk image.

In my case, I saved the whole installer app (the same as downloaded) in an external disk before installing it in my iMac. Now, can I just copy the installer to my MacBook Pro and run it with no trouble? Or should I burn the disk? I don't really intend to burn it now, using the installer would be more practical.
There is no reason that running it from the installer won't work.  That's the way Apple intended the installation to run, so that is probably the safest way to perform the upgrade.