they are when my story demands it either weak (the players are where they are supposed to be or where i want the story to go and so i let them take out the storm troopers with ease), or they are moderate (now the troopers have skill and somewhat decent), or they are elite (the players are derailing the story or scene or being nuts in say boarding a star destroyer and attempting to take one over with a group of 5 players only)

We haven't seen any stormies in my game yet, mostly due to the fact that my PC's avoid the Empire like the Plague. The GM's section notes them as being an isolated fighting unit, answering directly to the Emperor. So they would be outside of normal military command structure. They are cited as going through heavy indoctrination to ensure their fanatical loyalty to the Emperor.

Honestly, I see them as being a mid to high level threat for the PC's. I think most Imperial garrisons (Mos Shuuta not withstandind) would probably have a majority of Army/Navy types with a much smaller portion going to the stormies. They featured so prominantly in the movies mostly as a means to reinforce the "faceless" nature of the Empire.

Out on the Fringe, I think it's more likely that people would run into corporate security forces, thugs, and maybe the Army. I tend to save the stormies for when someone "influental" with the Emperor would reasonably have access to them.

In my games the stormtroopers are the imperial army. Organizationally I have them setup like the US marines. They have their own commend structure (with their own commandant) separate from the navy but are often under the command of naval officers.

Stormtroopers can be as little or great a threat as you want them to. As minions you can increase or decrease their group size. You can adjust their wounds and soak. You can add talents like Deadly Accuracy to make them tougher. Lots you can do to keep them as a challenge for your players.

Just to amend what I said, even though I consider the STs the standard imperial army there are different levels of STs. Some are the common grunts and some are in elite units like with the clone troopers (I.e. commandos, ARCs, etc.).

Storm Troopers are an eilte core. The reason they are often seen in the original movies is due to the importance of the events. Stolen plans to a top secret project? time to bring in the marines
Personal guard to the Dark Lord of the Sith, aint going to regular military
launching forces on a proven military threat bases. heck the Elite are better than using guard duty

event after event shows there is a good reason for the Storm Trooper to appear int he movies. The movies represent the big threat and big hero's.

As for the Clones. I believe they had accelerated growth. most likely didn't make it 10years post Revenge of the Sith. With maybe a few with rare mutations.

....and sturn points out a very good point with images

if you make the biggest threat common, then they become less of a threat. it's a ho hum encounter. Might as well be fighting goblins on the open field

The Emperor's Royal Guard also did occasional rotations as regular stormtroopers, so once we've got stats for those guys, you can always sneak 'em into your ST squads.

http://starwars.wikia.com/wiki/Imperial_Army

Solo addressed this a bit. It seems that there was a military, with stormtroopers in reserve, but over time they were phased in as both a symbol of fear, and simple ease of access.

Ahem. This is a Star Wars forum. The correct image is

I always use Stormtroopers depending on the location and what works best for the story. For example, while my Gang was trying to bust someone out of Wobani, the troops were hardened elites who bled Empire.

Meanwhile, at the installation on a small, unimportant planet in the Outer Rim, they were more lax. The CO was a die hard Imperial, but most of the rank and file troops were local boys and girls who were just looking for a job and to get some benefits while they were young.

This just helped to flesh out the world a bit for me and my Gang, since not everyone in the Stormtrooper legions are going to be die hards, and a great deal of them are just looking for a job (IE, the character in Twilight Company for those who read that book, or Han Solo in the movie). Combat against them is treated the same either way mechanically, but story wise the Out Rim guard are more likely to save their own skin than to die fighting for the Empire, while the more dedicated soldiers are going to fight tooth and nail to see their Emperor's plans carried out!