Quoting New & Interesting Insights Into Google Rankings & Spam from Pubcon:
It May be Easier to Walk Away from Banned Domains
Sites that Google's webspam team has severely penalized or banned entirely from the index can be very difficult to re-include, and thus, Matt suggested that "walking away" and "starting over" may be a more prudent strategy. In my opinion, this is largely due to link profile issues - if your site has a "spammy" link profile, it's tough to ask an engineer to sort out the wheat from the chaffe manually (or algorithmically) and stop counting only the bad links. Thus, re-consideration requests may not be as effective a use of time as registering a new site and trying to re-build a more trusted presence.