I’ve pocketed about a grand in the last year and a half, just by switching current account and hoovering up the joining bonuses.
Generally, it’s a matter of filling in an on-line form in about 20 minutes. No difficulties transferring direct debits. All very easy.
Had a few issues opening an account with Lloyds TSB, but these were unrelated to the actual switch itself. Furthermore, they were so eager to throw compensation at me, I made almost as much as I did from the opening bonus.
Edit: They contact your employer for you to divert your wages. However this is the one aspect I tend to be “belt and braces” about, so I fill in the internal form at work too.