Thank yous after the wedding, but try to get them sent out within about 10 weeks. Hard work, but longer than 3 months and people complain (well, my mother complained that XYZ hadn't received one after 6 weeks, but I had loads to write and sent them all at once... imagine one aunt getting a letter 3 weeks before the other!).

Your registry is the last time you use your maiden name. If you so wish... you can keep using it!

It's easy to change your name - I tended to visit all the organisations in person and they copied the certificate themselves. The odd place I couldn't visit accepted photocopies of the certificate. The car insurance changed my name 2 weeks early as my insurance was renewed on 4th September (we were married on the 18th) and I didn't want to pay the £50 for a name change, so they were really good about it and didn't want proof. Oddly enough, the mobile phone was the hardest one to organise! So I cancelled it as I no longer needed a contract phone.