I've installed the latest CrossOver 3.0.x. Just installed Act! 6 (2004) and the update 6.0.3. So far most things are working fine. However, I have found these problems so far.
1 - When restoring a database, you are asked for your information for the "MY RECORD" record. If you choose select (if you already have one in the database), ACT crashes.
2 - Many of the fonts are the wrong sizes
3 - ACT appears to run slow when doing keyword searches (this could be my system, will have to verify soon)
This is it so far. The other problems that I have encountered deals with file permissions set on a windows box (where my production data sits). Once the data is moved to the linux box, all the permission problems seem to vanish. More updates as I find them.