Can you define 'incompatible'? MongoMapper is hardly incompatible. Maybe not 100% integrated, but I'm using it in a Rails 3 project, and it works just fine. I'm also using Mongoid in a Rails 3 project, and while it's definitely more integrated, it's hardly the only option for Rails 3 + MongoDB.

Very interesting. It makes you think about more things when you are comparing cloud services.

The other half of the discussion is: Does it really make any difference in real world applications? I suppose that's the question you always have to when dealing with artificial benchmarks.

On a side note, what script are you using for the image lightboxing? It's amazing!