I know there's some friendly folks over in Redmond who like to read SEOmoz, so I'll make this as short and painless as possible.

The MSN search engine currently uses link neighborhoods to judge if a .com site is targeted internationally (like, say - to Canada). So, if lots of links point at your .com site from .ca domains hosted in Ottawa, even if you want to be targeting the US, you might not show up at all in MSN.com and instead, rank at Sympatico (or MSN.ca - they're a big provider of Internet service up there).

So, let's say you're a clever spammer with some new competition (or some older competition who doesn't have too many links). And, let's say you also have access to a good number of Canadian links. Sound like a recipe for trouble, eh?

(sorry - couldn't resist...)

p.s. Thanks to a little bird for news on this one. You rock, dude :)