This plugin, along with the gold cart, used to be my favorite solution for basic eCom through WordPress.
Now I find myself spending more time trying to fix fundamental issues with the code in the plugin than I do building a simple store. The basic shopping cart functionality does not even function properly anymore, without hacks. The last few updates have turned this smooth and simple plugin into a shambling mass of JS and PHP errors.
The support forums are dying, premium support forums are "temporarily offline," and the developers are nowhere to be found. What can be done?! I've wasted too much money on multiple Gold Carts to abandon it completely - I've still got to support those old installations - but I can't waste any more time going forward with this plugin.
So, I think all I can do is warn you. There was never any real documentation to begin with for this plugin - and now it is severely outdated and nearly completely incorrect - and if you install this, thinking it will be an easy way to setup a store - prepare for headaches.
If you are upgrading to 3.8 from any older versions, prepare to have your entire theme broken - without any documentation on what has changed in themes, what works and what doesn't. I guess they expect us to just check out the code in the new theme and adapt.
And I must recommend you do not spend any of your money on any of the "premium upgrades," at least not until Instinct/GetShopped can come out of hiding and possibly explain themselves.
Rest in peace, WP-E-Commerce! I'm going to Cart66!