New kids on the block: an analysis of modern blockchains [Technical paper]

It is not exactly interesting to read as it is just an overview paper with very few useful informations. It however demonstrates the need for decent whitepaper about Peercoin, as current one is obscure and outdated.

Conclusion of the paper:

...Peercoin, meanwhile, has switched to proof-of-stake long ago. Despite there being no formal analysis of its proof-of-stake mechanism, it does move considerable assets around, albeit two orders of magnitude less than Bitcoin. Both Namecoin and Peercoin have very few clients; we showed furthermore that their bootstrapping process relies on unavailable seed nodes.