Arno Blumer (Upfront systems) recently moved to Europe from South Africa. His first experience with plone was a simple project planning application, just with tasks with a duration, people who could do the tasks and some charts. At some time, a client had very specific project planning needs, so they made a second much more elaborate system, including invoices, milestones, contacts, etc.
A nice feature he showed in the demo is the quite elaborate kss editing in for instance cost estimates: You can add rows in-line; change items; all the costs and numbers are kept up-to-date constantly.
The application was continuously developed over a three-year period with client input. They tried to keep a "core" project manager product separate from the actual client implementation. That turned out to be very hard: keeping everything separate. A couple of core project managers were the result without an easily-distillable real core product that can be released on plone.org.
Arno's conclusion: what plone provides is a means to develop something that fits the client's needs like a glove. You can mold the system further and further based on client's input. Long running projects get increasingly robust as you have real-world input all the time. Also the open source nature of plone helps in seeing continuous improvements to plone itself: a lot of companies contribute back customer work to plone.
My name is Reinout van Rees and I work a lot with Python (programming language) and Django (website framework). I live in The Netherlands and I'm happily married to Annie van Rees-Kooiman.
Most of my website content is in my weblog. You can keep up to date by subscribing to the automatic feeds (for instance with Google reader):
If you'd like a tool for managing your projects, you can use this application inspired by David Allen's GTD:
http://www.Gtdagenda.com
You can use it to manage your goals, projects and tasks, set next actions and contexts, use checklists, schedules and a calendar.
A mobile version and iCal are available too.