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The TTL is 1 hour and the site is a high PR7 if that matters.
I shall look forward to some comments on this.
This topic comes up very often here, take a look at some of the threads that a Google site search [google.com] returns.
Executive Summary: Google will completely ignore your TTL :(
The good news is that Google have improved their DNS retry times significantly. I think it was in response to webmaster concerns.
These days, IP change problems seem pretty rare, but I'd still advice keeping a site up on the old IP for a while.