Clonetroopers
I got an explanation for why the Stormtroopers are so crappy even though they were cloned from Jango Fett.
The great part about the Clonetroopers is that you can't disable all of them just by knocking out a Control Ship, yet you can manufacture an unlimited amount, just like droids.
Well...eventually, when the Jedi wise up and figure out Emperor Palpatine is the bad guy, they launch an assault on the cloning facilities on Kamino, which halt the production of more Clonetroopers.
This speculation is supported by a quote from Rick McCallum, sometime after TPM, in which he stated George Lucas was thinking of having some huge water battle somewhere. And since Kamino is largely water, or all water, a battle on Kamino may have been what George Lucas envisioned.
Now, why did Darth Sidious choose to have the clones manufactured on Kamino? Perhaps the cloning technology is exclusive to Kamino, or atleast scarce throughout the galaxy.
So when the cloning facilities were destroyed, the Emperor had to start the process from scratch. Perhaps the new cloning facilities were built in a hurry, and thus just plain wasn't as good. The Emperor probably also had to use a new template, maybe somebody not quite as skilled as Jango Fett, which *could* exlain why the Stormtroopers were so inept.