I tested PauPress (including the Pro version) for use on a basic inbound marketing site and ended up using an alternative CRM plugin suite. PauPress is better suited for membership sites or simple storefronts where CRM features are needed, but it will not support traditional lead/demand generation where visitors get a link or download in exchange for a form they submit.
Leads tracked through PauPress forms become WordPress users whose profiles can be customized and accessed by customers/members on the front end. This is great if you need it but totally unnecessary if you don't want to use PauPress for a store or membership site.
The strongest and most unique feature in PauPress (compared to the alternatives) are the complex custom logical search filters you can build to drill down on your users/leads.
The worst thing about PauPress is that all forms must be displayed in a panel rolled out from the top or bottom of the page. The developer states (in early 2014) that normal form embedding in the page content will be possible soon, but until it is you cannot create a standard landing page.
The rollout panel is not a common interface design patterns for forms for a good reason: it is confusing, repetitive, and eventually annoying. You can end up having your visitors spending a lot of time pulling down the panel and interacting with it while it covers up your core content. The panels will also cause problems with themes using design elements like sticky menus.
Additionally, the PauPress styles for forms are non-standard and not very well designed; they will override your theme styles, and there is no support built into the backend for shutting them down in favor of alternative styling. I didn't see documentation on this either.
The backend interface for PauPress takes over the normal WordPress user manager and adds several menu items with several pages of tabs. The organization is not terribly intuitive, but it's passable.
In sum, I would say this is the second best CRM option in the plugin repository now, but it is built toward a niche use-case: sites that need a good, basic CRM tool with ecommerce capabilities. It will be substantially improved once the mandatory dropdown panel is retired or made optional.