Convert older Unity project to Unity 4 problems?

I was wondering what impact it would have to upgrade our project to Unity 4. Our project is due to be released somewhere in december, so I want to be really carefull with major decisions like upgrading to the next Unity.

I’m especially affraid that all our custom shaders/materials will be ruined, let alone our particle systems and other graphical stuff.

Does anyone has any experience on converting project to Unity 4, and if so, did it give you any trouble?

Any kind of help or tips are greatly appreciated, since I want to make this decision pretty soon.

Thanks in advance, Tim

What new features in Unity 4.0 does your game need in order to ship?

Do you have QA time to re-start all the testing from scratch?

What increase in revenue do you expect to make as a result of your expenditure on upgrade costs?

We upgraded our project to Unity 4 from unity 3.5 and have encountered an major problem. Unity 4 begins converting our old project and right at the end it crashes and unity is unable to reopen (unless holding alt at launch and selecting a different project). We have an open bug report on the issue and they have been able to reproduce the results but it has not yet been resolved. We have had to go back to 3.5 for the time being until a solution is found. This seems to be a rare problem bit is something to keep in mind, definitely keep a backup of your project before converting if your move to Unity 4.

the same shit for me. Just crashing on my project.