I have a site with very good results in google for lots of keywords! This is a site in 2 languages.
The serps are all based on the .be (belgium) domain name. What we want to do now is do a restructure.
the .be should go to the dutch part of the site (instead to the english part) and the .co.uk domain name should direct to the english part. Thus changing the entire site domainname pages.
Both domainnames are in use at the moment but both direct to the root (english part), so the only change would be the .be redirect. could this hurt us? Do not forget that all traffic from google comes from .be because this is our main serps listing.
Keep in mind that google is having problems handling 301's correctly now. I redirected a directory from one site to a new domain and google handled some page correctly but others not. For some pages they now have a supplemental result on the old domain and a url listing on the new. Also keep in mind that while this is a completely different scenario from what you are doing, I lost all my Google traffic because the new domain is in the sandbox. If you have substantial Google traffic that is important to you I would be VERY certain this isn't going to put you in the sandbox before doing any major domain restructuring. This thread [webmasterworld.com] has a bit more on the 301 problems.