I just tested this. It seems that entropy collection takes very long time indeed. What a pity. Apparently there's just a kernel buffer that contains gathered entropy, and consuming that entropy allows me to see that it will be replenished rather slowly. So the statistic munin graphs me is not the rate of entropy generation, but merely the amount of available entropy.
Somehow this multi-gigahertz multi-core machine and all its myriad peripherals together are not harvested for more entropy than about 10 bits per second.