So far I have seen no issues other than the wonky timecode display in the dashboard. I have worked on a couple of small projects with no problems.
Things I have noticed:
Promise Pegasus2 is 100 MB/sec faster both read and write. I have done nothing except update FCP X and OSX.
Application and projects open faster.
Relinking is much faster.
All of my plug-ins work fine so far. I do not use AU plug-ins in FCP X so that is not an issue for me.
Next week I will be pushing harder and see if I find anything.