I bought a parked domain that was first page google for a specific keyword. Actually the keyword was the url. I pointed some of "my own" relevant decent PR links to it and now it's gone!!! Any suggestions on what might have happened? This is "whitehat" all the way. They are all my sites with orginial content and good links.
It will definately come out, as to how long this takes no one can saw, could be week or could be months. I think if you keep adding links and be patient you will probably see even better search engine results for your keywords once the domain comes back out of the sandbox.
There's no standard formula on the sandbox. Just keep on working on the site but don't go crazy or you may trip a spam filter.