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In the meantime don't make the change until you have an understanding of the implications of the move. We made a change in 2 sites in early October and one was missed completely for the latest update in Google. If you can leave the existing server as it is until Google does it's deep crawl (should be soon after the update - ours was around Nov. 3 this time around). Then make your DNS change and leave both sites running for a least one cycle until you are sure that Google has updated their DNS cache and is crawling your new server. It has been pointed out in this forum that it can take awhile for them to find your new location.
Another concern is if you are moving from MS to Linux. If so there are other problems related to Linux being "case sensitive" in their urls while MS is not.
To sum up it needs a little planning and study before you make the same mistakes that I did.