I've received a response to my ticket saying that the withdrawal must have become stuck in transit and that they would chase it up at there end. I don't even know what this means.
This may be of interest to you:
http://gendal.wordpress.com/2013/11/24/a-simple-explanation-of-how-money-moves-around-the-banking-system/tl;dr: plenty of room for problems in the system of sending money between banks.
Even more so with bitcoin related businesses. I got an email from my bank about a transfer to btc-e, two weeks after it was stuck at a intermediary bank because they suspected fraud.
I never had problems withdrawing from Kraken. If you read the announcement thread, you'll notice that the majority of deposit/withdraw problems were due to banks or users entering incorrect or incomplete information.