My understanding is that bad neighborhoods=Google banned sites. I’ve read alot of posts about gambling sites being “bad neighborhoods” too, but it doesn’t jive with the SERPs for gambling terms. Google definitely rewards gambling webmasters for gambling related terms. Maybe people posting about our sites in general SEO forums are saying people in our industry tend to employ more black hat techniques than in other industries, so therefore beware of any gambling sites. Not really sure, just guessing.
As for checking a Google banned site, the easiest way to do that is to check their PR. If the Google toolbar is gray (meaning PR0), then the site might be banned, otherwise it is brand new, or hasn’t been indexed. This is one reason why it is very hard for a new webmaster to get links off the bat with no PR showing.