I just took another look at WP-Ecommerce's page here. I got a chuckle from a guy who called it WP-Crap-Commerce - his comments were like mine, but much blunter. "beta quality..." "a month working around errors..." and so on. My experience was nearly identical to that.
Can someone install it and very lightly test the basics and have it work? Obviously, yes. But if you have to develop with it and use a large number of its features, you're in for some $%$%$$, and don't say I didn't warn you.
I can't recommend that with a straight face. The one thing I'll say in anyone's defense regarding ecommerce for WP - because of WP's infrastructure, and many users' very heavy reliance on plugins, it's a wonder anyone can get it working at all. So it's a tough job.
But if you have a plugin with over a million downloads, but a rating of only 3 stars, that speaks volumes. WP is so popular that there is a demand for basically anything that will "kind of" work for ecommerce, and they cruised into that niche. Do they have consultants? Sure, how else are you going to get more than the simplest functionality to work?
If I were going to try any sort of WP ecommerce, I would most likely try the plugins that use FoxyCart, a nice 3rd-party shopping cart. I know Foxy works well from having made sites with it. Because it's really separate from any system that's calling it, there's a very good chance of it actually working. They support loads of payment gateways, are adding features all the time, and if anything goes wrong, they're on it really fast. What a concept! Nothing like WP-Ecommerce. I won't say that WP users are cheap, but many will balk at Foxy simply because it does cost some money per month.
That said, if I were going to do serious ecommerce, like a really complex store, I would never consider WP for that. And I'm a huge fan of WP.