Really dunno what you mean by this, but the registry won't be removed from Windows 8 / 9 and everything that follows.
It doesn't really matter, since in almost all cases, even if the registry gets really, really, really, huge (I use a lot of dev tools, VMs, have many games and applications installed.. and I haven't noticed anything), you will most likely not notice the slowdown it causes, because, really, a second of slower Windows load time really isn't noticeable.

These are good if you uninstalled a program and it didn't clean up after itself, leaving lots of hanging file associations or "load on startup" calls.

But that's rare as heck nowadays. Windows 7 is not Windows 98...

Are you sure about that? I thought they were already in the process of removing it. You know on account of it causing far more problems that it really solves.
I've seen it happen myself. I'll have tons of software installed and uninstalled and you definitely notice a significant speed up when all that gunk gets removed from the registry. It's not just the load time, it's the additional time that it takes the computer to process the enlarged registry.

There's also the related issue of registry fragmentation.

All in all, there could be another explanation, but what you're saying really doesn't match with my experience using Windows over the last decade and a half.

Well, IIRC, Windows takes like 0.0018 seconds to open, read, and close 100 registry keys, so... you do the math. :p It could have been something with the registry, but I doubt that the amount of keys was the problem.

I don't doubt that that's how that supposed to work, but in the time I've used Windows, I've run into all manner of bug and corner case. I'm always somewhat skeptical when people make those sorts of strong statements about a MS design decision when they still haven't figured out how to make a version of Windows that doesn't go tits up if the system drive gets its letter changed.

Personally, I'd rather give you something more concrete than anecdotal evidence, but there is a prima facia argument for the cleaners working under certain circumstances. In general though, I don't doubt that you're correct about it. I've noticed that most of the time there's no cleaning needed, provided you don't regularly add and remove things from the registry via install programs and that you have sufficient space to avoid fragmentation.

I use CCleaner as well. Works wonders, but your should really format your pc and do a fresh install every year or so. Keeps everything running good.

CC Cleaner works great. HiJackThis! has a pick-and-choose registry cleaning function BUT beware when doing so with it if you haven't made about 3 backups of your registry and don't know what you are doing.

Remember kids: registry diving is for trained professionals only!

with educated users and proper maintenance and you'll never need to re-format. Its all about how you install/uninstall how often to defrag your file system and page-file and if you allow the MFT to go out of control. Also how often you get in there and really clean and re-apply thermal compound.

I use Comodo System Cleaner. Safe and easy to use:
http://system-cleaner.comodo.com/

Basically, i love Comodo products because they're free of charge with full feature. Comodo Firewall is one of the best firewall out there, lots of customization and tweak that can suit various people's need.

That's probably true these days. But, the thing is that it shouldn't require special steps to keep the system going for an indefinite period of time without reinstalling. That's mostly a Windows only thing as I've never had to reinstall FreeBSD or Linux because I'd been using it for a long period of time. They typically are a lot smarter about how they handle software installation and system maintenance.

Very true... my Linux machines go and go...

I think it has to do with the fact that in Linux and *BSD, the configuration files are per application and for user applications per user, stored with the profile. Meaning that it's unlikely that they'll interfere with each other.

The main thing to watch out for is during updates, but I can't recall ever having had trouble with a Linux distro since I got one with a sane package management system.

Most of the problems I've had with Windows over the years has had to do with the random commingling of files and settings requiring a minor miracle to separate.

Registry "cleaning" is not necessary and should not be attempted, whether manually or automatically. Any perceived benefits are imagined. In the case of an actual problem with the registry no automated tool will fix it for you; in such cases try reinstalling the program in question or using System Restore to reach a good working state.

If you want to make a real difference in performance, try disabling worthless startup items (e.g. Adobe ARM), third-party background services (iTunes, Google Update, ATI Hotkey Poller, etc.), and browser addons (e.g. Skype Toolbar). This takes only a few minutes and you'll see a real, tangible performance benefit without that snake oil after-taste.