I have a site which has quite good Google positioning, http://www.christianbits.co.uk
I purchased the equivalent .com domain a few months ago (christianbits.com), so that people can use either address.
I have updated the DNS entry for the .com so that it automatically brings up the pages on the .co.uk domain. The domain shown in the address bar when you do this is .com; however, there may be some internal links within the site that mean that people will end up in the "real" .co.uk domain at some point as they naviaget around.
Am I likely to suffer any penalties from Google as a result of this? I could try and find all internal links that specifically point to .co.uk and change them to be non-domain specific, but I don't want to do all that work if it is not necessary.