I spent a few years of my early adolescence making lots and lots of HyperCard stacks. All those hours spent with HyperTalk and experimenting with layouts and process flow benefit me to this day.
If anybody else 'round these parts used to spend a lot of time with HyperCard, I'd be curious to hear their thoughts on how it has affected their current work, along with any whale tales of monster stacks.
I found that both tools were incredibly productive and actually made it much easier for me to jump to Lisp because I was already familiar with things that would seem 'magic' to programmers using more traditional tools. The productivity, dynamic features, and 'macros' had me programming circles around some of my competitors in my niche at the time. Many people thought the Card tools were toys, but they allowed faster development than anything out there and my compiled stacks STILL run faster than, say, Java. Yes, even today. I know this because I benchmarked it recently. One company is STILL using the MetaCard-based ERP system I wrote, and a video store chain is still using a POS system I co-wrote.
When the MetaCard technology was sold, I moved on to using a tool by the buyer of the technology, a Scottish company called Runtime Revolution. By that time, I had discovered some other tools that were also very powerful and I was focusing on mostly web apps, so I stopped using the Card technology. (Even though the tool has internet features built-in.) I still know some companies that have great products on the market that are secretly based on *Card technology, though.
If you are really into HyperCard-type technology, you should check out www.runrev.com. In some ways, it is still ahead of many of the alternatives. In fact, I have an enterprise license and a training book that I'm not using if you want to contact me. There is also a Python-based Hypercard-like system around that you should look at, although it is much more primitive.