Tim Cook, Ray Ozzie, and a host of others have proclaimed that we're in a "post-PC world." Well, not quite yet, but you can see it from here.

Like it or not, the post-PC era looks a lot like the iPad, Kindle Fire, Xbox 360, Roku and any number of smartphones. While these devices are way better for some tasks than traditional PCs, we stand to lose a lot in the transition as well.

Let me be very clear at the outset. I'm not saying that tablets, consoles, e-readers and the rest of the post-PC devices are bad. Like many others yesterday, I fought with Apple's shoddy online store to place a pre-order for the new iPad. What time I do spend watching the tube is usually courtesy of Netflix or Amazon Prime via the Roku.

But as tablets and other devices expand functionality to the point that they replace PCs for many users, they're stopping short in ways that matter a lot.

The advantages to our new post-PC overlords are pretty obvious. Most of us who've futzed with trying to set up a PC-based media center of some kind will gladly adopt a Roku or Apple TV instead. They can do almost everything that a PC-based media center could do, but are much cheaper and dead simple to set up.

Forget About Upgrades

But the simplicity comes at a cost. Check out the comparison of Roku models. If you happen to have been an early adopter of the Roku SD, you're stuck with no wireless support, 480i max resolution, and so forth. If you're a late-stage adopter, you don't have the option of getting component output or S-video with newer models.

In short, where you could usually upgrade or retro-fit PCs depending on your needs, the Roku and post-PC products are much less forgiving.

Likewise, I'm writing this post on a 17" Dell laptop from 2007 or so. In tablet years? It'd be destined for the scrapheap. The battery's nearly dead, but if mobility was important enough to me I could easily find a replacement. I've upgraded its RAM and hard drive at least once, and if need be I'm pretty sure that I could swap out the mini-PCI Wi-Fi adapter for a faster one.

If this thing was a tablet? Forget it. You're saddled with the original hardware, period. It's too early to say with certainty, but I'd be willing to bet that in five years time Apple won't even support the original iPad with iOS updates. The original iPhone – not quite five years old – is already obsolete.

PCs become hopelessly obsolete eventually too, but you're talking five to seven years in many cases not two to three. I know folks who have pushed their PCs past the ten-year mark by a combination of tender loving care, upgrading everything that could be upgraded, and what must be the patience of a saint. Odds are if you see an original iPad in 2020, it's going to be in a museum, not in use.

And it's not just about upgrades. Let's think about peripherals. When I ponied up for the new iPad yesterday, I had to choose between the AT&T or Verizon model. Imagine for a moment having to choose between, say, Comcast or AT&T when you buy a PC. Nuts, right? But if you're picking up an iPad with the hopes of replacing a laptop, you're also saddling yourself with a carrier for the life of the device as well.

On PCs, you could swap a peripheral and move from Verizon to AT&T or Sprint, whatever. Not so much with the tablets. You have a little flexibility with peripherals, but mostly, you're stuck with the options the manufacturer gives you.

Lockdown and Lock-in

Tablet users are much more limited in what they can run on the tablets than PC users have been. If you're using one of the many Android tablets, you can usually run CyanogenMod if you'd like a newer or more open version of Android than what comes on your tablet – but that's really about it.

The current plan for ARM tablets running Windows 8 is require Microsoft-signed operating systems.

You can choose to jailbreak your iPad, but good luck getting Android on the iPad. (Best I've been able to find is a Cydia theme for the iPad.)

Really determined and knowledgeable users can hack pretty much anything. I'm not saying that it will be impossible for anyone to get more out of a post-PC device than the manufacturer intends.

But the last few generations of hackers came up with computing devices that were much, much more friendly to experimentation and maintenance. No doubt, plenty of parents will see to it that their post-PC kids will still have hack-friendly computers in the hopes that they'll follow in hackerish footsteps.

But the devices that are or will be replacing PCs in most households? They're decidedly unfriendly to hacking. Ideally, kids (or anybody, for that matter) would be able to write programs to run on their primary computing platform. But the iPad, Kindle, and the rest of the lot are essentially run-only platforms. Yes, if you have an Apple developer account and a Mac at home, you can write programs for the iPad. But I suspect there's going to be a lot of homes in the near future that have iPads, but no PCs.

The Downsides of Apps and App Stores

Speaking of applications, there's essentially zero application portability between platforms. Buy a copy of Angry Birds on iOS and you'll be able to carry it from iOS device to iOS device as long as it's supported. But if you buy it on iOS and then switch to Android? Tough luck.

PCs aren't without problems in this regard. If I buy a game or application for Mac OS X, I don't have any good way to run it on Windows or Linux. But you do have plenty of options for emulating or virtualizing Windows on other platforms if you need to carry your Windows apps with you to Mac OS or Linux. Developers are unlikely to even have the option of offering emulation or virtualization on top of iOS.

The app stores make for simple purchasing and installation of apps, but they're also putting a barrier between developers and users. A lot of developers offer licenses that work on Mac or Windows, but working with users across iOS and the Android stores is much more complicated since the developers don't have a direct relationship with users.

The limitations that app stores put on developers has been raised quite a few times, so I don't think I need to stress that too much here. Suffice it to say that the post-PC world looks pretty bleak when it comes to our ability to run any application we want.

I know for many users, the post-PC world will be just fine. You might be one of them. But overall, I think we're losing something as we embrace computing appliances over general-purpose computers.

(Image from the Apple II History page.)