Yes I have changed and am currently doing so again. It all went very smoothly. They moved all payments for me. HSBC is currently offering £150 to switch and another £50 if you're still with them after 12 months, There are conditions. Have a look at Moneysavingexpert.
I was amazed how long it took to set up a new account (over an hour at the bank filling in forms plus three thousand supporting documents) and then some of my direct debits or standing orders just disappeared which caused chaos (and an argument with Specsavers who told me to my face I was a pain for purposely cancelling my direct debit for contact lenses and were sarcastic cunts when I told them it was the banks mistake... and breathe...).
When we switched to nationwide everything was switched over apart from a problem with 1 direct debit but that was the recipients fault as they didn't claim from the old details or the new ones and then tried to charge us for their mistake!