Well, I don't totally agree.
I jumped from 10.0 to 10.2 in a "single" jump (well, they were more like lots of mini-jumps). I ended with a workable installation, but with a few packages which had been removed still wandering around.
The basic is to run in single-user, upgrade glibcs first and then the pkgtools, then I went upgrading a/ l/ and ap/, and then everything else. Between every step I've made a few checks to make sure nothing was wrong (I can't remember if anything went wrong at somepoint... but I'd bet it did). I read the HOWTOs on upgrading Slackware before and after (to make sure I didn't missed a thing). And then started reading through the changelogs (both, 10.1 and 10.2) to remove stuff which should not be there and some special notes which Pat might have made.
Also: I didn't update kernel stuff (kernel nor alsa) when I did the jump (I was running a custom kernel anyway).
If you ask me, it is a BAD idea. It's much safer to make a different partition for /home (where you save your data) and /usr/local (to install custom software) and /, and just reinstall over / (AND make sure the installer DOESN'T format /home and /usr/local).
But if you are willing to the danger... go ahead, remember that even if you end up with an unbootable system your data should still be there... you will just need to boot from another media (like a LiveCD or a USB disk/pen or the Slack 10.0 CD2) and copy valuable data and either reinstall or try to fix the problem (I'd prefer the later, it's a rewarding experience when you just fix something screwed
)
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EDIT:
As for your Slackware -current question I just need 2 things:
-A web browser (or kslackcheck which could be found somewhere in the kde-look.org site) to look the Slackware-current change log (
http://www.slackware.com/changelog/current.php?cpu=i386)
-I like to use Slackpkg to keep up with Slackware -current (it comes in the extra/ directory of your CDs or favorite mirror). But be aware that it could bring you back to a pasture/ version of a package if you're not careful enough.
Slackpkg could also help you to upgrade to 10.2. Look /etc/slackpkg/mirrors for info.