I have done everything on my main desktop to get Lightroom CC & Photoshop CC working normally except throwing it in the trash and starting over. It is running Win 7 64-bit, 16Gb memory, plenty of hard drive space (SSD for the OS & Programs, traditional HD for data). Both Microsoft and Dell have exhaustively tested the system over the past several weeks. The OS has been re-installed so it is fresh.
I have scoured the Adobe forums, I have Chatted with Adobe Tech Support, and I have had Adobe phone support where 2 different techs remoted into my computer to assess the issues. On Thursday, May 28, the Adobe tech promised to call me back on Friday, May 29 at 10am my time. He said that Adobe knows of the problem and has a solution. He must still be searching for the keys to the solution because it is now June 7th and Adobe has not called back.
Microsoft and Dell (I have paid tech service contracts with both) have officially given up and referred me back to Adobe.
I can usually get the "Server Busy" error in LR CC to go away after anywhere from 2 to 10 minutes. Photoshop will become responsive 2-5 minutes after opening. The performance degrades after working about an hour and it is slow to move from one module to the next, to do keywording in the Library, to use the Adjustment Brush, etc in LR. In Photoshop, I could go out for coffee while the Lens Blur Preview came up.
Adobe, this is just plain unacceptable. I know I'm not the only customer with this issue. We need a fix and we need it now. Tech Support needs to own the problem and be responsible enough to follow-up.
Been having the same problem with the update today. Thought it might be windows 10 but same sluggish behavior in windows 8.1. Multiple reboots and the same thing. Lightroom kept crashing and not allowing imports, along with the bizarre server busy error. Realized that everything was slow so I decided to unplug my usb 3.0 card reader and suddenly everything started working. No crashes and everything seems responsive so far. No idea why but this worked for me.