This leaves me with three possible reasons for the diggs disappearing.
1. The people who digged it only want to be associated with very popular items. If they digg and the item does not go on to get hundreds of diggs they undigg. If this is the case then this behavour would seem to damage the idea of digg being a tool which can highlight good information from sources which don't have the clout of say, CNN or the BBC.
2. The people found something else I had dugg that they disagreed with and as a protest undugg my other submissions. If this is the case then it's against the spirit of digg and what is the point of this kind of protest if no one leaves a comment to explain why they have undugg.
3. Maybe some people just like digging stuff then undigging it?
It's not something I am going to lose sleep over, I'm just curious. I would suggest to digg that perhaps they might encourage people who undigg leave a comment to explain why. If nothing else this would help other diggers decide if they want to digg an item or look at it at all.
Anyone out there got any ideas?