I was wondering if anyone here has any experience with ColdFusion?
Matt is right, I have many years' experience with CF -- in fact, it's the only platform I code web software from scratch on, though I sometimes install Perl or PHP scripts/apps for specific uses.

I am thinking of purchasing some shopping cart development software that comes in three flavors – ASP, PHP, and ColdFusion. I wouldn’t have hesitated at purchasing the PHP version, but these guys are raving about ColdFusion so it just made me curious.
If an app you're looking at comes in these flavors and you are already familiar with PHP, it's a no-brainer -- especially if it's OSS and you might need to hack it a bit. In my experience, CF has vast advantages over PHP, but price is of course not one of them.

Even though there is a free developer’s download of ColdFusion 8 - it only works locally. Matt can correct me here, but it seems that you must then purchase the server side software, which is pretty expensive.
This is true.

So, what do you think? Is it something that is so great that it justifies not only the learning time involved, but also the expense?
If you want to reduce your coding time -- or your dev team size -- by 2x - 3x, CF is worth the investment and learning time. Most people believe it is far easier to learn than PHP, and the scripting syntax is mindbogglingly simpler.

But that doesn't make it a good solution unless you want to start seriously coding in it. I would say that about any platform/language -- don't "learn" it if you're just going to dabble in it, and don't pay for an expensive platform unless it's going to pay off with other dividends, like the ability to offer unique packaged solution to your clients (unlikely with CF, since most types of apps are also avail in Perl/PHP/RoR/JSP/ASP, etc). The real reason to learn/run CF is to be able to code robust applications very rapidly. It's superior in most ways except it's expensive and it's not open source (if you care about that, which I don't).