I got my first PDA about 4 years ago or so. The gadget freak in me was crying out for one, but I made several trips to the store to convince myself that I really could write into it directly. It turned out to be easy to learn, so I was hooked and got a Palm III.
Supply definitely created its own demand here. All of a sudden all of the stuff I needed to remember could be tracked with minimal effort, and backed up with a few keystrokes. The memory volume was such that I kept about every address, phone number, or other trivial bit of information in it fairly effortlessly. Bye bye Day-Timers.
Then I met somebody who had a better one, and a camera to work with it. Shortly thereafter I dropped my Palm III and it never recovered. I took this very well because it was my excuse to make a beeline to the electronics store and buy the next one, with more RAM and more apps. And of course, the digital camera module.
The camera led me into sin because it was so easy to take candids - you could point it and nobody would know. But the resolution wasn't so great, and although it took color pictures, you couldn't display them well on a grainy grayscale screen before downloading. They took a fair amount of RAM too. That was an older technology though - I might have to take another look.
Then about a year and a half later the alarm function acted flaky on the new one. A saner person would have spent more time investigating, and eventually I figured out what the problem was - I had changed a setting inadvertantly. But no, I had lusted after the color devices and I wanted rechargeable batteries, so it was a Visor Prism for me.
I've only had it for a couple of months now, but now the Treo has come out. What do you know? - I just had some trouble with the Prism after dropping it...
Actually I really did - the charging system was acting funny. But a little surfing on Handspring's website and an in-charger soft reset fixed the problem, so my baby goes back on the road again. The worst thing about the Prism is that it's fatter and doesn't have the built-in flip cover, so it lives more dangerously in my shirt pocket - I make sure the screen faces my chest. But the battery recharges rapidly, and although the screen isn't as sharp as the ones on certain Sony Cliés, it's ok. The next gotta-have features are probably vibrating alarms, higher screen resolutions, and better printing/syncing capabilities.
Nowadays you can get shrinkwrapped apps easily - BugMe, PocketQuicken, a spreadsheet, AvantGo...life is good. If you want hardware some is probably available at a Best Buy or CompUSA. You can get phones, modems, GPS, Ethernet, barcode/mag card readers, games, electronic books (dictionaries, PDR, Bibles...), even a massager and power-napper. There are also full-sized foldup keyboards or the little thumb-keyboards like on a BlackBerry. I suppose a full-blown docking station can't be far off.
I've never tried the non-Palm alternatives. The day could come. But I expect the devices will be far more trouble-prone, and you don't want trouble with a PDA. It's just supposed to work flawlessly when you whip it out until it becomes second nature.