As a follow on from my last post, here is a link to Matt Cutts follow up on the somewhat strange and regionally challenged UK SERPs.
There is also a theory that this is a legacy thing from the Vince update. I am not so sure. I think Google just underestimated the difficulty in matching the .coms, .nets, etc. to generic queries (and some not so generic ones too… unbelievably) based upon region. However, I think the thought process from what Vince was trying to achieve has played a part.
Looks like they are now taking this a bit more seriously though, so normal service should be resumed soon(ish). I guess all you search marketers with affected sites and actual companies this is affecting will just have to sit on your hands until then! Frustrating eh?