Bernie asked:

>  I've just ordered OS X.
>  Does anyone want to share tips, warnings, bad experiences,
>  do's & don'ts, etc re upgrading.

Bernie,

If at all possible, I heartily recommend having two hard drives (not 
just partitions), one with Classic installed, and the other with the 
OS X full install. Here is why:

In the case of serious directory corruption on the OS X drive , there 
are minimal tools available to repair the disk. Apple provides "Disk 
Utility" on the installer disk and as an onboard repair utility, but 
it is about as useless as Disk Doctor. Also, anything run from the 
Apple OS X installer disk runs slow as molasses. Just finding 
available drives can take 5 to 15 minutes!

You can also try booting directly into UNIX by holding down Command/S 
at startup and running the UNIX file repair utility:

/sbin/fsck -y

Here is a basic tutorial on using fsck:

http://docs.info.apple.com/article.html?artnum=24501

However, if you get a "keys out of order" after running fsck, you are 
stuck big time. As far as I have been able to discover, there are no 
OS X or UNIX tools that allow a recovery from a "keys out of order" 
directory corruption. (Believe me, I hope I am wrong here and someone 
can offer an OS X or UNIX solution.)

In the case of serious directory corruption, Apple's solution is simple:

Reformat the drive and reinstall OS X.

This translates into: "If you don't have a backup, you're hosed."

HOWEVER...

If you have a second drive with Classic installed, you can run the 
latest OS X savvy version of Alsoft's DiskWarrior from it and repair 
even the most serious directory damage on the OS X drive. And 
DiskWarrior will see the OS X drive, even if it fails to mount. (Why 
not just run DiskWarrior from its own CD instead of bothering with a 
second drive? I have had problems trying to boot from a CD with a 
hosed OS X drive, short of yanking the drive's IDE cable.)

Under Classic, DiskWarrior usually completes its work within a couple 
minutes. but repairing OS X drive directory damage may take a half 
hour or more with hundreds of errors reported. So far the technique 
has worked every time.

One problem we face as developers is that we are doing things with 
our equipment that the conventional user will never do. We may write 
code that just crashes the FB^3 compiler's OS X memory partition, or 
takes down the entire OS X. One thing I have hated about UNIX is its 
susceptibility to directory damage in the case of crashes and and 
power interruptions. (For instance: OS X permits the 
command-control-Power key restart, but here is Apple"s warning: Don't 
do it!) We all better get used to checking for OS X directory damage 
on a regular basis, more than we would ever have worried about under 
Classic.

The only other advice I have concerns mindset:

Under Classic, the user owns the machine.

Under OS X, the OS owns the machine.

The sooner you come to grips with this reality, the easier the 
conversion to OS X will be.

Ken