What do you want to do with this potential notebook? Would you not be better off with something bigger with more oumph? It's hard to give you suggestions without knowing what you do with your computer.
I could be completely off with this (since I don't know what you want) but here's my screen analysis.
Things an 11" screen is poor for:
-document manipulation. You want as much vertical space as you can get. If you do a lot of writing, having to pan around the page trying to find a specific paragraph or line is inconvenient. Having it sitting right in front of you with the text you're working on makes it much easier. One could argue that having a higher resolution screen can improve your writing.
-general internet browsing. Spend some time with a 15" CRT then move to a 20+" LCD. I'm guessing you know the difference already. Think about how much you would need to scroll to see the contents of a forum or blog like engadget or Gizmodo. Sure, you'd be able to see the white edges of the page on the sides, but not the vertical content. The web stretches better than it did just a few years ago, however. (smartphone explosion, mobile designs)
-iLife work/Logic/FC. I found GarageBand somewhat gimped with 1280x800 on my 13" MBP. Although 1366x768 ends up being more pixels, the problem was with the vertical pixels, not so much the horizontal.
-programming. I'm not sure if you're that type of person, but it's exactly the same situation as document manipulation.
-multitasking. Try opening more than one than one window on that thing. You will absolutely need to make heavy use of Exposé and Spaces. That's what they're there for. The trouble is that you have no other options without the addition of a secondary (and far less portable) monitor.
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gaming. Real-time strategy games like StarCraft and Civilization are hurt by the lower resolution far more than any other games. You'll find yourself scrolling around more than you would with a larger screen with a greater resolution. Remember, games run better on Windows. PERIOD. There is no fighting this simple fact. OpenGL simply isn't up to par with DirectX in terms of gaming performance yet.
Things an 11" screen is tolerable for:
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multimedia absorption. Movies will be great on it assuming you can stream content to it fast enough.
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gaming. Think flash games or typical iPad games. FPS games can be played well to a certain degree because they are largely resolution independent.
Remember that this applies to both the Air and the M11x.
I'm willing to elaborate more on any of these points or anything else if you wish.
