Unless my calculations are a bit off, I thought that with neutral luck, we should expect ~7 blocks daily - the CDF hits 50% at 3 and a bit hours IIRC.

8 blocks in under 4 hours! looks like the luck fairy has finally returned!

I'm running a number of Block erupters and one Antminer U1off a RasPi - after some experimentation, I found that if you have a decent air flow over the Antminer to keep it cool, the best clock ratio for mine is x0a01 - if I use the 'maximum' clock of x0a81, it hashes at 2.2 GH/s but has quite a high hardware error rate, at x0a01, it hashes at 2.1 Gh/s with virtually no errors (currently showing 0.03%!)
You may find that different devices give different error/hash rates, so this is just my $0.02 - you definitely want to overclock them if you have cooling though! I reckon 5 Antminers should be giving you at least 10 GH/s

I bet the conspiracy theorists and complainers that ran to another pool are kicking themselves now, especially since the hashrate fell by about 10% and our payouts went up.

If there was a problem, you wouldn't have been getting shares.  If Slush had been keeping blocks for himself, they woudl show up on blockchain.info.
So yes, pure luck. Read up on gaussian distributions.

I had a 0.01 payout yesterday, so I'd query this with Slush if I were you - make sure your payout address is right, and if it isn't what you expect it to be, change your account password right away!