I just wanted to chime in with my 2 cents on this thread, even though it will probably be the same as other peoples response (thread TL;DR)
I bought C8P literally 5 mins after it was released onto the Steinberg shop and started into it almost immediately. I had extreme issues with my midi in/out, sync, massive crashes, you name it. Instead of troubleshooting, I reverted back to 7.5.2 in a huff, livid that my paid upgrade was basically useless.
When 8.0.5 came out, I rejoiced and prayed that all the issues I had encountered on day 0 would be fixed. Alas, I was wrong. In fact, I seemed to be experiencing increased problems.
Anyway to cut to the chase, I did a complete reinstall of my OS (Mavericks), installed C8P (8.0.0) and carefully tested each plugin to see what would be causing any problems. I still had issues with my midi but narrowed it down to a problem with the active settings on my virus ti synth in the midi preferences. Deactivating this has solved my problems with midi.
Additionally, I found that NI Replika was a massive culprit in causing extreme crashes in C8P. It would affect performance and would stop projects from loading if there was an instance present in the project at all ie it would crash before even loading up the project arrangement window.
I have since removed Replika, I’m not that bothered as it was a freebie and to be honest I prefer the Vengeance Delay & Cubase’s own delay. I am still experiencing some crashes, mostly when I try to open a C7 or C7.5 project and occasionally I have problems opening projects in 64bit mode. Running C8P in 32bit seems to be solid enough to be able to work on, although I am still getting a few crashes per day.
I did try the update 8.0.5 but this was causing to many crashes so I rolled back. I will patiently await the next update.
Overall, I am pretty happy with C8P (8.0.0). As I have already said, I do get some annoying crashes, GUI on vsts going black, opening piano roll etc on big projects tends to turn the screens white (this is a strange one) BUT I am no longer screaming for blood at Steinberg. There are some amazing features in C8P, render in place is such a god send and really has increased my workflow. The instrument & mediabay racks are a novelty at first, but I have since removed them as I don’t feel they are needed if you are used to key shortcuts (F5 mediabay etc).
I’d say i’m about 80% happy with this version, which I think for a 0.0 release, thats pretty good lol. I eagerly await the next update to see if the major flaws have been addressed, but in the meantime C8P is usable and happy with that!