I just tested the new version on my localhost server.
OK, First let me say that I do backup my database and I do deactivate my plugins before upgrading.
Since the version number 3.0 suggests a major version release (which apparently isn't the case), instead of over-writing my files I removed the old before installing the new.
Went to wp-admin/upgrade.php - All good, then ......
Nothing in the browser, nothing in view-source. OK, what other changes did I make that might have caused a problem?
My old config file didn't have the "salt" DEFINEs so I had added them. Commented out the new lines, nope, still the WSOD.
I checked my wp_options table's active_plugins, that was OK, renamed my plugin folder to TEMP just in case even though I had deactivated them, nope, still the WSOD.
Then I found the problem. Every upgrade so far has had the Default and Classic themes in the Theme folder. Not so with 3.0 it only has the new TwentyTen theme.
No wonder! I can't expect the blog to show with no Default theme to show it!
I'm always careful to not remove my plugins from the wp-content folder. And I don't use the Default theme on my live blog so this wouldn't have happened there. But having fallen into this mistake makes me feel like such a newbie I really should know better than to take anything for granted.