Looks like I'm going to forage ahead in my research into using mongodb with the DataMapper mongo adapter from solnic, if only for the reason that it was the first interface to my mongodb server I was able to get working!
Now that I've got it working, I'm realizing I've gotten a bit rusty with DataMapper in the few weeks that have transpired without having used it. I really liked what I saw so far, and was only distracted by these new "NoSQL" document storage systems.
In retrospect I find it a little ironic that I've circled around again to DataMapper!
Anyway, back to dm-mongo-adapter. It seems heavier than I expected, and so I read up on the MongoDB Ruby driver and thankfully its super simple! Seems like the equivalent of a supercharged memcached client.
I've just run through a very simple comparison and I like the bare driver better. Its super simple and the startup time for my Sinatra app is much faster. No doubt, the dm-mongo-adapter is cool, but it sort of brings me back to what I'm exploring away from (hence the irony I mentioned earlier). I still want to get my datamapper skills back in shape, but my experiments with mongodb are not the right time.