I'm impressed that your account is a whole 5 minutes older than your post. I'd be even more impressed if Parse was open source instead of yet another walled-garden PaaS hyped by shills.
It would definitely be cool if they open-sourced the platform, but, in the meantime, you might be interested in this project:
http://code.google.com/p/openmobster/wiki/learnmore
Personally, though, I don't mind paying for a service like Parse. If someone is willing to not only build the features I need but also to wear a pager and get up at 3am just to keep my users happy, I'm more than happy to give them some of my money.
My only wish was that I could place an easy API layer between Parse and my app, because I would want more fine grained control over how data is mutated (even with ACLs, someone with write permission could mutate data and corrupt it if desired).
There's a REST API, but I don't think I would want to use that as much.
Here's some data I exported from one of my Parse accounts: https://gist.github.com/2475461.
Deploying APIs in the cloud for primary use in mobile apps is an oft-repeated/able task, and it doesn't seem like there's anywhere near enough value in the Parse API on top of what you get from the native SDKs and a solid combination of open source stack software supported by an enterprise track record more promising than a Series A round a few months ago.
Also, as the comments here suggest, there are a lot of slight modifications to the default use case that reward having solidly built a stack not built on yet high-level PaaS abstraction. Sorry, but a JSON representation of your data is the low bar, not some instant proof that the product is magic.
In terms of value ... I'm really not sure how you lose - if your app is a flop you're going to coast along on the free plan, if it's a success you can focus on your app rather than your stack, and you can migrate away from them when you feel like it.
I'm not advocating Parse open source anthing, it's entirely up to them but open source does not mean $0.