So, I've done searching on the Katana shock, but I've still got a few questions.

When the rear is raised due to the shock, how much is the steering affected. With a one inch raise, that seems like it would make the GS handle more like a race bike.

Also, how much does the chain tension need to be adjusted?

Is this even worth doing for a guy weighing 140lbs?

I weigh 200 pounds and the stock shock worked fine for a while, if your stock shock is too soft so the suspension depresses several inches when you sit you 140 pounds on, then you probably need a Kat shock, or simply a new shock, also if you're doing 2up with a heavy pillion.

The raise doesn't afect the bike very much, you could simply put the stock shock on the 7th notch and would notice the same effect. The chain adjustment depends on how thight is it right now, so once you install the kat shock check the chain. It also depends on how stif you set up the new shock, set it up on the milder side and will barely notice the change in terms of geometry.

Good luck!

I am a 190lb guy and stock the rear felt a little mushy.  I ceanked the preload to the 7th setting and it feels firm.  Then again this is my first bike and i can only compare it to the touring bikes that i learned on (silverwings) many years ago.  

If it is an older bike I would replace it, if not try adjusting the preload.

The front seems ever so slightly less stable on the highway. Only barely noticeable though.

Also, it leans you forward, putting more weight on your arms (or more strain on your back to keep the weight off your arms).

The progressive springs are a common good match to the kat shock, there is a lazy way to replace them, which includes only taking off the fork caps and replacing springs and spacers, also fork oil level check up. The long way includes disassembling the front fork and replacing fork oil, what is not that bad, just keep handy a torquemeter to tight everything back to specs.

Yeah, I'm looking more into the progressive springs rather than a Kat shock right now, seeing as how I'm a flyweight. I'm going to jack the preload up to the highest setting and if that doesn't make enough difference, then I'll spring for the kat shock. The front end is just too soft, and the progressive springs will be a welcome change.