... Isn't there a bridge over that, in some film recently?

I've worked for 2 major international banks in the last 2 years (and been present for a DR test at a third) and the 50% sounds about right.

At the first the attitude was "Yay - for the first time we've managed to get SOMETHING to work after spending a whole weekend trying to fail over, shit get everything back where it's supposed to be for monday morning trading"

At the second they don't do DR tests, because the DR solution is not actually separated out from their normal sites (e.g. they have 3 main sites in the UK, and each can run the other's stuff if necessary) and therefore testing it would be a bitch... They're also pretty sure that it would "just work".

The third party DR test I was present for had about an 80% success rate for the business applications - the failures were related to remote working and security policies. They treated this as a failure of the test, and will be re-running it in a couple of months to confirm that they've fixed it.

So I'd say that out of the massive sample set of 3, 50% sounds fair ;)