Same domain, different extension

do you still need a 301 re-direct for these?

[fom2001uk]

I know the safest method for dealing with multiple domains is the 301 redirect, but is it still necessary for identical domains with different extensions? (e.g I have a domain.com and domain.co.uk).

Domain.com is the original and the one I promote. The UK domain is just there to catch UK users who automatically put .co.uk at the end, instead of .com

Do I still need a permanent 301 redirect from domain.co.uk to domain.com, or will the spiders realise this can't be duplicate content?

[tedster]

If you serve the same content for either domain name, then it really is duplicate content, although innocent in its intent.

That said, it doesn't necessarily mean you will have a problem, but then again, you might. (Not very definitive, am I?) It takes Google a while to sort out duplicate content and decide which pages it want to return - a good bit longer than just a normal indexing cycle in most cases.

I recently ran into a problem with two .com domains (hyphenated and non-hyphenated versions). Had been no trouble for years and then the rankings started getting all tangled. My troubles began when several "overnight" directories sprang up and began using either version of the domain name, willy nilly. The two versions began to develop different backlinks, different PR and eventually, missing pages.

If the .co.uk is only there for type-ins, then I would take the safest path and do the redirect. Why tempt fate?