Being able to build 50+ nightly ROMs per day requires a huge amount of processing power. Back in February, the team lost its access to the cluster it had been using, but was able to raise enough money through donations to be able to purchase 3 Dell R610 servers. Those servers are each powered by two Xeon X5675 CPUs (12 cores total) and 32 GB of RAM, which apparently are so beefy that they can build CyanogenMod 9 in just 9 minutes. That's some serious speed.
Even better, the new servers are online and ready to start building ROMs. The only thing left to do is to put together an automated scheduler so the team can be able to announce the builds predictably, then we should see a whole bunch of new nightlies being pushed out.