After much searching, I still have questions:

I want to install CentOS 6.3 on my machine. I have used CentOS 6.2 and 6.0 in the past and when I update, I install, the newer over the older, i.e. 6.2->6.3... In doing I have to back up my home dir and then, sometimes, restore it which is a pain... I install quite a bit of 3rd party software and libraries etc., and usually put them in /opt

What would be the best partition scheme if I want to either 1) continually install latest greatest CentOS, or 2) change linuces often without screwing over my home dir and other apps I have installed.

My usual partitoin scheme is something like this (I have a 1TB drive and 8GB RAM), and I don't care if I make partitions too big, but if I am being absolutely wasteful, and the partition sizes are larger than could ever be used please let me know too)...

I see no issues with the partition scheme you have above, the only other thing that some people would suggest is to separate /var into it's own partition so if it fills up it doesn't crash the / filesystem. But with 150GB that really isn't a huge issue for you.

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200MB for boot and 25GB for root should be more then enough.

You do know its safe/supported to upgrade in-place for minor versions eg 6.2=>6.3 for RHEL/Centos?
Its only major 'updates' eg 5.x => 6.x that they insist on fresh installs ?
Of course, taking a backup should be done regularly anyway.

Personally I don't like to divide too much; probably just scared that I run out of space somewhere while still plenty of space elsewhere.

On servers, I use a separate /var (not containing webpages and databases) and /home and that's it. Not said that it's perfect, but it works for me.

Instead of trying to figure out "the best and only" partitioning layout, I suggest you look into LVM. The idea is that you can create, delete, resize your "volumes" instead of partitions at will, even on a running system. In most cases, you can even have /boot on an LVM volume.

Actually, /boot must either be on a std partition or RAID1; LVM is not an option according to the docs I've read.
https://docs.redhat.com/docs/en-US/R...de/ch-lvm.html

grub2 can boot from lvm.

I can confirm this works, I have a few systems on RHEL that are running GRUB2 and boot from a lvm without any problems.

OK; something new then. I always use the default.

@Wim Sturkenboom
that's the first thing that you have to learn; don't multiply partitions needlessly (sort of a paraphrase of Occam's Razor, but there is no evidence that William of Occam knew anything useful about partitions...or Bacon and Brown sauce sandwiches, either).

This should work, if you are doing it right (you should only need the home backup if something goes wrong, but that is not an argument that you do not need to backup home...I usually have more than one usable backup, and don't use them, but I still need them).

To do it right, you have to leave the home partition as it was (same start, same finish, same file type and don't format), and it is probably advisable to leave all of the partitions doing the same thing as they were previously.

Restoring home has another potential 'gotcha'; if you restore hidden directories, you will restore settings for a lot of programs. That might work and save you (some) time, or it might fail and leave some programs un-startable. Probably, some of each. I'd rather make a new install a clean start, as far as program initialisation is concerned, but it is up to you. You can always delete the unwanted hidden directories for programs that do cause subsequent issues.

(And, one other question; you don't intend to multi-boot Linux distros, do you? If you did, the advice for sharing home dirs would be different.)

/boot is way larger than it need be; I've used 220M in the past, and was being generous; swap is larger than it need be. In fact, while you possibly don't need any swap with that amount of ram (you could check whether you use any...) I'd still advise a small amount of swap, so that if something does go wrong, it 'fails gracefully', but 2G would certainly do that.

(Side note; is this a 64 bit installation? you may not be able to make full use of your ram if it is 32 bit.)

I don't really see the argument for separating /opt and /usr/local on a general purpose workstation (see Wim Sturkenboom's comment); don't make the partitions and they will fall under '/' automatically, and you won't have the possibility of getting the size wrong, provided that '/' has enough space (and it does).