To be rather undiplomatic about it, I think that they are junk. They are essentially subdomains with little brand recognition. If you really want to target the UK or the US then use .co.uk for the UK and .us (or .com) for the US.
Just the best ones eg casino.us.com or business.us.com
as they are too expensive. The .uk.com are much better known in the UK and
eu.com again only the best generics :imho: :imho: