This is the theory by which I will eventually migrate from 2.0 NBR to 3.0 NBR, once it's released.
I have not tested this, yet. I'll report back once I have.
But, it's a good start to make a plan before exercising it.

BACKUP:
Full Images Backup:
Before I do anything, I will take images of my two SSDs following this process I've outlined in the past:
http://forum.eeebuntu.org/viewtopic.php?p=8581#p8581

User's Folders Backup:
I will then backup each of my user's folders for safe keeping, as well. I'll do this while still working from "Try" mode in a USB boot-up of Eeebuntu.
In this example, I'm archiving the user alanb's folder:

Preserve List of Installed Software:
As documented here, I will preserve a list of all applications installed on my system, using Save Markings As ...

I prefer this to the command-line method noted in other threads because it only preserves what is to be installed. Applications requiring other items be de-installed will happen automatically when packages (like Wicd) are selected.


Preserve List of Installed Wine (Windows) Software:
If you installed any programs under Wine, make sure you obtain a list of those programs, as well.


Preserve List of Sources:


INSTALL 3.0:
Follow the same procedure you followed to install 2.0.

Update, Update, Update:
Once booted into the full installation, run the Update Manager until you have no more updates to load.

Wicd:
I do not know if this will apply to you, but I had many issues with Wicd playing nicely due to Python 2.6 being installed under NBR 3.0.1 and no existence of Python 2.5 and/or 2.4. So, I personally ran Synaptic and installed Python 2.4 and Python 2.5 to completion before I installed/re-installed Wicd.


RE-INSTALL/RESTORE:
Re-Install App Sources:
REMOVED - If you have "other" sources to add, so be it. But, do NOT replace old sources for new ones.

Re-Install Linux Apps:
As documented here, I will restore my list of all applications installed on my system, using Read Markings

Re-install Wine Apps:
If you installed these from Windows' .EXEs, you'll need to do it again.

Restore Users' Folders:
I, personally, extracted the TARchive into a "tmp" directory and then hand-picked the items I wanted restored to my home folder. Why? Because some settings of some apps (in hidden directories/files) have settings based on older versions of software.


Again, this is still a theoretical procedure I was going to follow. I don't have a ton of productivity on this system, yet. So, reinstalling things manually was a lot less issue than the first way I attempted to install all of this stuff. If you decide to try this procedure, please post feedback and I'll update accordingly.

More guides in the wiki, too.
Good to place it here, too.

I erased my 2.0 and put on 3.0 base. Can't wait to see how this LXDE is gonna turn out. I'm not bothering tweaking base because I know I'm not gonna keep it around much longer.

Here's one thing TRiPgod mentioned worth linking:
Keeping all your programs after upgrade to 3.0

HOWEVER, File > Save Markings is resulting in a zero-size file. What gives?

Well, if you check the box "Save full state, not only changes", then you get a file with a complete list of what to install.

But ... using the command dpkg --get-selections > /media/USBstick/installed-software, you get a complete list of what to install and what to UNINSTALL, too. You can then use the GUI (Synaptic) to read in the "markings" save with the above command. A bit of a hybrid action, but a more complete solution, the way I see it.

OK, I'm done updating the first thread and the title ... for now.
I'm looking for a brave guinea pig

I could always go back and start from scratch and test the theory, now that I've got a full 3.0.1 NBR installation fully configured as I had it before ... I just did things more manually because I didn't have a ton of things with which to deal.

But, it would be nice to have an automated updater in the future. I hate the whole re-compiling of the BJNP driver for my Canon MX700 with Cups, for one.