A forum thread at WebmasterWorld named Longest You've Been in the Sandbox?, which first required me to post the previous entry named Google Sandbox Defined: Sandbox = Ranking, Not Indexed, also discusses the time frame people have been finding themselves stuck within the gates of the Google Sandbox.
Skip over the first several posts, because the users is misinformed about the definition of the sandbox. I'll post some of the stats and somewhat, terrifying messages left in that thread.
Launched in early May, first spidered by Google in May 2004 - 12 months in the sandbox.
I have one site which has been in [the sandbox] since December. But this recent "update" seems to show a little encouragement as some of its pages have jumped 200+ positions on one DC (and no they had no change whatsoever on the pages and no huge difference in backlinks).
10 months now and still waiting.
Site launched in February 2004. It was a move from an old URL to a new URL so the content was identical when it launched (of course I changed it since then). It came up ranking very close to the old site for a couple of weeks and then went into the "sand box." Over the year I was able to achieve high rankings on related terms but not the primary terms. I was able to get the primary terms into the top 100 but not the top 10. After just about a year, rankings were finally "normal" (top ten for primary terms).
Site launched in September 2004. Again, some terms rank but not as high as I think they should. I believe that the site will be out of the sandbox this fall. Time will tell.
First crawled in Dec. Average position for main target KW, page 280-300. This went on for 4 months. To date, absolutely no-where vanished entirely out of the search results.
That was just the first page, continue reading from the second page on. Come on, Google.