Finally... some good news.
The developers have informed us they've found the cause of the performance/stability issues. The client should now be functioning normally. Please report back here if you have issues relating to performance of the client or if you find any bugs.
If you have suggestions for improvements to the software, please post them
here. I'll be monitoring that forum also, to ensure all the good widely-supported ideas, are passed along to Merge. In fact I have just received some positive feedback from the developers on a number of the key changes many have requested in the last 24-48 hours.
Once the client is stable, as it appears to be now, Merge will start rolling out other minor bug fixes and improvements to 6.0. Thanks for your patience and understanding everyone. I wont crack open the champagne just yet...maybe a (tentative) celebratory lemonade for now.