I always leave smudges on the screens of my cameras, and I have noticed that the smudges come off the screen of the 5D MkII way easier than any I've had. FWIW.
I changed the Canon cover on my 1dsmk2 today. The hardest part was getting both sides of the protective plastic off of the double sided tape Luckily my wife makes greetings cards as a hobby so she gave me a roll of the perfect tape to replace the scrunched up mess I made of the original
Out of interest the damage to the 1dsmk2 was caused by zip on a jacket during one walk.
It`s just that the 5D2 screen is so large and looks so vunerable but that new unprotected screen on the 1dsmk2 is just so clear (well! as clear as a mk2 screen can be)
Certainly the 3M stuff is spoiling the 5D2 look so that must go. Now , am I brave enough to go bareback with that 5D2
I also changed the clear window on my 24-105 today where it had been cracked( I just put it down on top of a coat in my car boot/trunk for a moment and it rolled sideways and touched my tripod just at the right spot)
This is the first 920,000 pixel display I`ve had and I see vertical rainbow lines. Obviously it`s only on the display and doesn`t affect the images.
The 5DII and 50D LCDs have a contrast enhancing, anti-glare coating. It probably interacts optically with your screen protector. I get similar effects on LCDs when I wear polarized sunglasses.
I gave up on stick on screen protectors long ago. They usually ruin the LCD image by making it dimmer, murky and often impart a colorcast. Just watch out while wearing western style shirts (metal trimmed buttons) and belt buckles. They can really tear up the back of a camera. I use a handstrap so my cameras rarely touch my torso.
I'd try a different screen protector. I have come across some brands that do not play well with color LCDs so I relegate them to protecting my top LCD.
To use or not to use? Well, that's like the filter or no filter debate....
Few of us (I'm guessing) would prefer a glossy LCD on our computer LCD's, and I feel the same way about my camera bodies. boxwave.com sells some very nice matte-finish screen protectors, and I use them on all my bodies. I see no degradation of image quality (doesn't the 50D have the same LCD as the 5D2?), and the loss of all that glare is a big improvement to my eyes. Also, much less prone to finger and nose prints
bka20d wrote:
no you are not alone!!!!
in answer to your question #3:
i use giottos aegis 3" glass lcd screens...i had them on both 5d's, i have one on my 1ds3 and one on the 5d2. the screen they make for the 40d fits the 5d2 perfectly.
and as a nikon shooter, yes i do use the cover that nikon supplies on my camera....
Well! as bka20D suggested I fitted a Giottos 3" coated glass screen to my 5d2 and WOW, what a beaut. Coatings to take away reflections and the pro version transmits 98% of light. Once fitted (apart from the small giottos insignia) you really don`t know you have anything attached and your screen is back to square one.
I must admit, I didn`t know about these that are 1,000% better than a film and very easy to fit and remove.
Luckily my wife makes greetings cards as a hobby so she gave me a roll of the perfect tape to replace the scrunched up mess I made of the original 
