Appears to be back to normal now.

It's a possibility for the future, but at the present time you can't deposit to Kraken through Fidor UK.

Seriously? This is somewhat unacceptable. Really.
People will lose their shirt on margin.

It was a DDoS, but connections issues should be resolved now.

All that is attached to the internet is violable (by its definition) but I think kraken has a good security 'system'.

Site seems to be down just as they where having nice volume on BTC.

It seems like you guys at Kraken can't handle the volume lately...

Service should be restored for all clients now. Since this was a DDOS attack, it was not caused by increased trade volume on the site.

I made a BTC deposit to one of my (used) kraken deposit addresses, but although it already has 10 confirmations on the blockchain it doesn't show up in my "recent deposits" tab on Kraken.
The deposit address I used is not expired or expiring by the way.

Should I worry?

A few days ago I also made a deposit to a different kraken address, and that one showed up as soon as it had a single conformation.

I'm out of Kraken ASAP. Simple as that.