So, based on estimates- it seems as though the "mystery pool" is about 700MH or so, which is a decent amount. Before yesterday, the net hash rate was somewhere around 2.5GH or 2500 MH. When the mystery pool is on the network, that means that they have a 28% chance of finding one of those big blocks, and the rest of the network has a 72% chance. However when they decide to sit out a round, we have a 100% chance of finding those smaller blocks, and they have a 0% chance. This means that our average block reward overall is lower, because we have a better chance at finding the smaller blocks.
Here's the thing though. When they drop off the network, you know what else drops? The difficulty. It reduces some of the damage done, because even though we're finding smaller blocks... we get to find MORE of them. Here are what our numbers look like over the past few days:
+------------+--------+-----------+----------+
| date | min | max | avg |
+------------+--------+-----------+----------+
| 2014-02-17 | 12,423 | 1,393,339 | 436,665 |
| 2014-02-18 | 15,009 | 1,463,166 | 446,819 |
| 2014-02-19 | 12,627 | 1,205,115 | 494,429 |
+------------+--------+-----------+----------+
We're still finding big blocks. We just have a slightly lower chance of finding them, like a 28% lower chance with the current net hash rate. If the net hash rate were to hit 7GH, that chance would drop to 10% lower, and if it were 14 GH it would only be a 5% difference- negligible. That's why nobody even notices with DogeCoin, because the net hash rate is so huge that it would be impossible for someone to get a lot of the big blocks. They can still decide that they only want to TRY for big blocks, but that doesn't mean they'll always get them.