Last June, I launched a product named Fast JV. Until a day or two ago, it had never shown up in Google.
My first thought way back when was that it had simply been sandboxed, but when I registered it in Google's Webmaster Tools, they said that no pages from the site appeared in their index.
I've read somewhere that when you're sandboxed, your pages still appear in the index -- they just don't come up in search results, or at least they're way, way down at the bottom. If you're not in the index at all, and you have inbound links from sites that are indexed, apparently that means you've been banned.
Why the site had been banned, I'll never be quite certain. My guess is that it happened because as soon as I launched the site, I added links to it from a bunch of my other websites, and either it got too many links unnaturally quickly, or some particular links looked to Google like paid links.
At some point, I saw in Webmaster Tools that you can request reconsideration of a site that's been banned, but the instructions say that you need to point out specifically what you'd done to fix the reason for your being banned. I didn't know what had caused the site to be banned, so I didn't expect that I'd be able to make my case successfully.
So I left it for a while. And then I submitted the URL in the regular form for submitting sites. And nothing changed.
Then a few days ago I decided, what the heck, I'm going to request reconsideration. I told them that I was unaware of ever having broken any of their rules, but that I suspected such and such was the reason for having been banned. I noted that in my mind I was just doing normal cross linking between my own sites.
And apparently they were convinced, because a few days later, the site was showing up in searches!
While I certainly wouldn't recommend trying to pull a fast one on Google, I have learned that a good faith request for reconsideration can be accepted even if you haven't "fixed" anything.
...except maybe I did fix the problem. I did remove the one link on one of my sites that was most likely to look like a paid link.