This is a clear case that sites linking to you can cause traffic loss.
Has your traffic recovered ?
Do you believe that Google had a applied this as an intentional filter ?
It really looks as though G set your trust to almost nil , before restoring it and I'm thinking that high PR links can set off a check of other factors which previously had slipped under the G radar.
[edited by: Whitey at 10:55 pm (utc) on June 10, 2008]