Are Unity 2.6.1 Projects compatible with Unity 3?

I started a game a few months back in 2.6.1 and now that 3 is out I'd like to know if it's possible to just open up my project in 3? I am using C# mostly with a little bit of Javascript that's being phased out. I am using a couple of bought scripts like iTween and Sprite Manager 2.

If it's not automatically backwards compatible, how much effort am I looking at making it compatible with 3?

This must be one of the most oft asked questions but I could not find it in my searches, maybe I looked in all the wrong places? I did a search here and on Unity3D.com.

Thanks in advance for anyone taking the time to answer my question.

Unity 2.6 projects are not fully compatible with 3.0, see the link Molix posted for details. We tried to make the process as smooth as possible, by automatically converting things where possible, so in most cases, upgrading should not take you a lot of time. Some things do require manual work, however - for example custom written Cg shaders will likely have to be modified to run in 3.0.

In any case, make a backup copy of your 2.6 project before updating it, because once you opened a project in 3.0, you won't be able to open it in 2.6 any more.

There is some good info about how to upgrade here.

FYI for iTween So far it looks like everything should be 100% the same. If anything fails with Unity 3.0 let me know and I'll fix it up.