well i can see this thread going in wrong direction...but this may not be bad
errorsamac was asking for advices about his site,so we should provide what we have here.
my site underwent same problem - but may not be caused by link building because that happened before i started to build links.
days after i finished on-page seo, one of my keywords ranked in page 1. not 2 days after, it disappeared, just like errorsamac's experience. and now (10 days after disappearance), it came back to top 10.
so i would suggest, don't worry and don't be hurry, especially when you are building links.
it seems like sandbox still lives...