I had asked a internet marketing expert on how to get a banned site back into Google. I've had had sites I worked on for years getting back links and achieving PR5 status banned and had no luck getting them reinstated. Here is the answer I got:

I asked Nancy your question, and here is what she
had to say…

You can actually get a site that's been banned (grey
bar plus no pr) back to a PR+ position. I've done it
where the previously banned site is now at PR3. But
the question is, should you? I'm finding that more and
more there is some element that even I can't define or
really even describe in Google's algorithm that seems
to continuously ignore and almost 'mistreat' certain sites.

If Google starts ignoring your site (it's not really
ignoring your site it's just that whatever this set
of attributes are that triggers filters is just too
hard to peg right now) I'm finding it easier to start over.

And that's what I'd probably recommend to you. Good news
is we know how to rank new sites without setting off the
filters that send you to the 'Sandbox' so many people want
to believe in.

This may not be what you wanted to hear but I hope it helps.

Take care.

Nancy
P.S. Take a look at the Area51 blog….

http://www.area51marketing.com/blog