I don't know about 1shoppingcart but remember, usually you get what you pay for. If you don't pay much usually don't expect fantastic support because they just don't have the margin built into their software price for it.
I have 1shoppingcartfree.com (free 30-day eval) running for a few clients as well as my own products. Some of the big internet marketing guys have bought a private label version of 1shoppingcart (tom antion with his kickstartcart, Alex, Armand). It's all the same product and support crew. Personally, I like their telephone support. I think I've talked to pretty much everone there and they have a good knowledge of their system. I've been using their system for 6 months and just discovered two more things it can do today. Pretty powerful system.
You will find "pain in the butt" stuff with every cart you use, no matter how expensive or cheap they are. I've been through 13 carts and this one gives me the 'least' pain in the butt. But, that's just me. Every situation is different.
One of the stranges things I've seen with carts is their flakiness working with payment gateways. I could have all kinds of things screwed up in my site, but at least when someone clicks the order button, I have confidence that their link to the gateway will work.