The user experience design in Maemo 5 / N900 does not suck. It comes with +/- the same amount of controls and things that people can use to build a new application (I'm developping for both Maemo and iOS). The problem that you see is that some people port other linux apps to the N900 without adapting to the new GUI - that's why we end up with an unusable mess of different GUI's :-) If everybody would use only Hildon or Qt, every app would look the same - Apple has much tougher quality controls, they won't accept anything that uses the GUI in the wrong way. So the fault is not with Nokia, but with the devs.

For your other points, as seen in the Nokia Forum:

"0) Why when all other phones are black on white background is there no such skin?"
Mod it yourself - it IS easy, but quite some work to create a new theme. Looks like nobody else had your need until now.

"1) Why is it so easy to go into screen edit mode so you accidentally delete icons?"
I too would prefer a better edit/unlock desktop mode, but it sure isn't bad enough to go nuts about it :-) And I think someone created a new version of Hildon-Home with better locking.

"2) Why is the address book such a mess? When you search inder All Contacts there is no ABC etc list on the right to enable swift navigation, unlike when you go into Select Contact from the calls list."
I just slide out my keyboard and type the first few letters. So quick and easy.

"And you cannot edit the pre-set labels like Home, Work, Mobile etc. Many people have different numbers in different locations and I want to be able to say Work 1 etc."
Correct, but more than enough different types to handle MOST situations. Also, it's often easier that people adapt their needs/process to an app than that the app adapts/includes every different possible use case.

"And to be able to read the blue micro-font as well."
Perhaps you really need glasses?

"3) Why is there no flight mode so I can use it aloft?"
Click the power button once. Then choose "Offline mode" from the menu.

"4) Why does the satnav need to be connected to work?"
I have no clue. Ovi Maps is absolutely shameful on the N900 and a disgrace for Nokia. The manager reponsible for this should have been fired LONG ago. And the one above him, too.

"5) The App Store is very confusing. Why does Nokia have this thing called Ovi? Why not put it all in one place along with Maemo?"
Ovi = Official Nokia app store, free or payware, closed source.
Maemo Extrase = Community app "store", free/donations, mostly open source.

"I downloaded the voice recorder to my phone but when my wife asked me to do the same for hers, I couldn't find it either by searching or listing all the Apps."
Go to the app manager on your N900, find the app in the installed apps, see how it is called and where it's coming from.

"App Stores are for extras, not add-ons or replacements that the manufacturer forgot about".
And where would you draw the line?

"6) Why when I try to enter something in the Google Search box (for example - actually most things in an <input ...> form) does the virtual keyboard not pop up?"
Did you enable the virtual keyboard? (Settings > Text input > Use virtual keyboard)

"I have to slide the little keyboard out all the time. Similarly after the update, I have to use the little keyboard to switch on the Send button for an SMS. "
I have a SEND button right at the bottom right of the SMS dialog. Don't you?