Recently I tried to migrate the website of the university I work for to Plone 4. The first thing I did was to checkout the development buildout from Plone http://svn.plone.org/svn/plone/buildouts/plone-coredev/branches/4.0. The alpha2 release is quite near, but I thought I can watch the changes/bugfixes better, when I use the development buildout.
The next thing I did was to include our custom and third-party products the site uses into the buildout configuration. This was the easy part, but running the buildout gave me the first error. It complained about some custom packages, which were not included as development eggs. We use the haufe.eggserver for our internal eggs and most of them were compiled in the Python 2.4 version. I took me a while to figure out I had to provide the 2.6 version of the eggs or the source-distributions. (BTW There seems to be a bug in both setuptools and distribute with the upload command in Python 2.6. They do not accept the -r, --repository flag and always try to upload the egg to pypi) For that reason I chose the source format and the eggs were recognized flawlessly.
Ready for the next step I tried to start the instance in foreground mode. Of course there were some errors. I had to use the Plone 4 branches of PloneFormGen and CacheFu and the the trunk of the PloneFormGen dependencies TALESField, PythonField and TemplateFields. In my custom products I had two errors occuring quite frequently:
Well now the instance with all dependencies still does not start because of the p4a.plonecalendar, which still imports the object events from zope.app.event. This is where I stopped today.... more to come ....