Are you hosting or planning to host your site in a bad neighbourhood?
It might be very difficult to determine if that's the case, but our free tool might just help you: it will show the most backlinked domains (by referring domains) hosted on any given IP or subnet.
Visually inspecting those domains can help you determine if the most popular sites on that IP are spammy and thus potentially dangerous neighbours to have for valid sites hosted on the same IP or even subnet. Our database is updated regularly and contains hundreds of millions of resolved domain names - give it a go!