Podio looks nice, has a modern UI, and is engaging to work with. The sound and toaster notifications can keep you hooked - we loved that feature!
We had some trouble sharing contacts within the organization. You can share a contact if you add it to a project, and there's a feature to import your Google Contacts that keeps them private to the user. With some work (maybe filtering contacts, because many may be irrelevant) and with the ability to simply share contacts without having to add each contact to a project, Podio could feature a powerful CRM component.
Podio's app customization lets you build powerful forms with many custom field type to closely map your data. This feature is unique to Podio among 50+ systems I've looked at, and with some improvements to functionality capabilities for the apps, it could definitely be a killer app. Note that Podio has a powerful API, and even though right now you can't use the API to modify Podio itself, if this gets implemented in the feature, that would make Podio the #1 customizable PM+CRM system.
Podio also has a Gmail contextual gadget, and this makes it one of the only 3 systems with both CRM and PM capabilities, API and Gmail gadget. The gadget lets you add tasks right now, but I spoke with the development team (who were very supportive), and they plan to integrate much more functionality in the future.
With the improvements mentioned above, plus Gantt charts, Podio looks really promising!