I'm pleased to report that the switch went without a hitch (was a little worried today because the fibre didn't come on to about half 5 this evening and at 1 point earlier I could make but not receive calls) but i'm proud to be a member of talktalk
I had exactly the same experience on migration day, except on ADSL. I was slightly worried that I had a several hours with a TT dial tone but no broadband as I had thought the two services might activate at around the same time, but it all worked out.