Couldn't agree more, robertmerkt.
I too had MANY problems with WPeC and went to the support forums for help. It was the same problems, over and over, that were still unresolved. Most of them didn't have any responses from developers.
I'm not naive enough to think that a developer should hold my hand installing this stuff or install it for me, but this is some of the worst support I've ever received. Even some of the free WP plugins I use have better support. After a few weeks of trying to get the plugin to work, I gave up.
I tried contacting Instinct for a refund and was ignored.
I posed in the "premium support" forum asking for a refund and finally got a response. I was told that the terms I agreed to when purchasing the plugin said no refunds. I was also told that any issues were due to a "poorly written theme" and were not because of the plugin. The funny part is, the theme I was using was a theme that was recommended on the WPeC website...
So here I am now, with WPeC that doesn't work, no support at al, and no refund.
I've since bought PHPurchase (http://www.phpurchase.com/) and am very satisfied. It installed and worked perfectly from the get go. I haven't had to use their support yet, but from what I've seen in the support forums, actual employees are responding to people in a timely manner. Best of all, they actually stand behind their product and have a 60-day money back guarantee, no questions asked.
Maybe WP E-commerce is a good plugin and I'm not smart enough or technical enough to get it to work. I really wanted it to work, but I just couldn't get it. I probably would have been okay with that. Not every plugin works for everyone.
However, the lack of support (and the fact that I am clearly not the only person with support issues) should be a big red flag to anyone considering spending money on this plugin. Buyer beware, if you can't get it to work on your own, you're screwed.