Hi Mirat,
It's worth noting that Python and Django are dependencies for piston, as well. And if you're using JSON, the only other dependencies are mimeparse and dateutil.
Honestly, I've been quite happy with tastypie (replaced piston with it on one project just last week) , as it doesn't conflate resources with models.
Don't get me wrong, I still like piston - it has a lot of great ideas. But it's certainly worth evaluating both to see which best fits your needs.
HTH,
In my first impression it has lots of dependencites, i usuallty think that if a library have much dependencies there is much chanse to have a problem.