I go through a lot of screen/entire body protectors on a lot of devices. I've used the following on the N900 and landed on a combo zagg invisible shield for the case and Clarivue for the screen. I tend to throw mine on tables, dashboard, in jacket pockets with keys so yes, the N900 plastic (and other devices) will scratch when you do this so I prefer case protection. The zagg is glossier than the matte finish, but doesn't look bad imo and protects it nicely if I need to return/sell it..

Lexerd: This one I haven't used before, but was one of the first available for N900. I always order two screen protectors: 1 for practice. Both were not aligned well: if you center on screen, cutouts were far off both horizontally and vertically. Both don't 'seal' on edges - partially raised on external and cutout edges. I don't recall seeing this on any other before. It does have a great look and feel. If it weren't for the raised edges, you could hardly tell it is there- cleaned, it is like a new phone out of the box. Application is very easy, BUT the adhesive attracts dust from the air like no other - the smallest, itsy piece of particle you can't even see is guaranteed to get on adhesive side. I ordered another twin-pack to see if alignment or edges would improve since I really liked. Same thing.

Zagg Invisible Shield: I've used this on a lot of devices. Like people say, the screen protector is 'rubbery' feeling. IMO, it is not ideal and does irritate me at times, especially with a stylus. I now primarily use these for body protection, but am paranoid of scratching the screen. Body installation has always been easy and no problem on N900. Not ideally cut, but it's the case so close enough. I have always had less trouble w/body, incl. no probs w/air bubbles, than the screen. Screen is a royal pain in the arse. Requires a ton of patience, very steady hand, bright lights and, ideally, latex gloves unless you want fingerprints (I don't care what zagg says about just keeping moist). I have yet to install one on the N900 that I get aligned right (I've had 3 so far) - one edge or another gets pushed against the raised rim. Two of the three got stretched during application. I admit, my dexterity isn't awesome and I do get impatient after the 3rd or 4th line-up attempt. If I am only looking at one screen with the zagg, I'll think "that looks perfectly fine." When I look at one of my others using nothing, a Clarivue or another brand that is a stiffer ultra-clear type, then I can see why not everyone likes the Zagg. It is noticeable and has texture (hold it at an angle - I've never not had texture on N900 or other devices). Great protection though and should be - just a little thinner than the protective clear stuff they put on the front of my car to prevent rock pits, under door handles to prevent ring scratches, on front of side mirrors, on side mirrors themselves, etc. and so far it's been great for that too - if you've owned a black car or ten, you know what I'm talking about. Good enough for a $__ car, good enough for a $700 phone.

So now I'm using a Clarivue anti-static clear for the screen/zagg for the case. Nothing to say about the Clarivue other than it just works, looks great, glides nicely - same as always.

I haven't tried it, but I suspect if you want the best of Zagg-style protection and glide of a Clarivue, you can use both. May prevent a few kinetic scrolling mistakes :-) (a benefit of the Zagg).