Here some more questions to ask of any potential system:
- if something better comes along, how much effort will migration away from the system be?
- how easy is installation?
- how painful are upgrades to new versions?
- how easy is it to back up your data?
- how much effort will ongoing maintenance be?
- how modular are the plugins? Do they require hacking the core code?
- how easy or difficult is it to create your own skin/template/look?
- how well-documented is the system?
- is there a community (mailing list/forum etc) associated with this system? How helpful are they?