I've just told Google to limit itself to 10 seconds between requests instead of the 2s it was on.
No idea if that's related to today's slowdown, or even how quickly it'll take effect.
Setting automatically reverts on 26th April.
Noticed it was slow earlier, thought it was 02 being shit.
Google says "Your request will take a day or two to come into effect." :/
So if it is Googlebot causing the problem it probably wont help much.