I was excited to use ThinkFree to collaborate on the specification for the project I was working on with the lead developer and allow sponsor to see the progress. Couple of good things about the app: 1) its compatibility with MS Office format documents was stellar and 2) the interface was fast and pretty convenient.
However, here's some flaws I've found: 1) the file locking meshanism is deficient. It will not tell me that the file is being edited before I open it. 2) file sharing preferences are only available on the file level - I would expect to see directory level preferences. And finally... the reason we stopped using it for our project was because it was not 100% reliable - a few times it corrupted the document :( This kind of stuff just can not happen for critical documents that several people work together on.
My other observation is that this kind of application should not be standalone.. It will fit in perfectly within a bigger collaborative project environment that has things like project calendar, tasks and other project related items. If you have multiple people collaborating on a document, that by definition is a project. The other thing these guys need to figure out how to do is to auto-save a local copy of the document on the writer's PC. There's absolutely no way you can afford to ever loose your work.