HU have given us an update on the technical issues, it sounds as if most things have now been resolved:
"Apologies about the issues on the site lately, and the frustrating experiences you've all had to endure.
The comments and answers showing up as negative numbers have now been fixed, and all blogs and questions should show the right numbers.
Second and major issue was the notification system. You all have received notifications that would take you straight to 404 page.. This was because the notification system for new replies, comments and answers were corrupted and every time someone made a reply / comment or answer on your community, it would send the notification, but with the details of some other community and / or older posts from your community; essentially wrong details.
We've resurrected the notification system again it is behaving as it should. Please ignore / delete all the corrupted emails that you've received since Friday. All the content posted in your community will be available under respective menus and are not lost.
Unfortunately, there isn't an easy way to correct those notifications and resend them, but the daily and weekly notification should have the right links.
Few users have also had issues with comments disappearing in the void - we don't know what the cause to this is yet, as it only happens when there's a lot of activity on the site. We've done some modifications that may take care of it (may be I'm being optimistic) and we'll be monitoring the site to see if we can replicate the behaviour again. If you have any problems with your content disappearing, please let us know.
Apologies again and thank you for sticking with us through the testing times."