I’m currently doing a shop using Interspire’s shopping cart and I have mixed feelings about it. The CP works really well (for the end user), but I do wish it was a bit easier to customize, the sheer amount of templates, subtemplates and snippets it uses to output even a basic product page is simply bewildering.
Community activity on the Interspire forums is close to non-existent, and, although you can e-mail support, the answers are often far from satisfying. Right now we’re holding off going live because of support for Ogone (a major European payment gateway), which is said “to be coming” in a next version with no ETA given.
And, for software of that price (the pro edition is close to 1K$) having to translate the language files for the CP and shop to Dutch myself is simply unforgivable.
I’m keeping an eye on Magento, but their templating system just seems weird (I mean really, XML based layout files?).