Everything is working fine today, but here's what was up. The problem only affected maps that are hosted by the New Jersey Geographic Information Network (NJGIN). My site just requests data from NJGIN, and if their servers are slow (or down), there's nothing I can do about it.
Next time you see a problem like this, check some maps that are hosted directly on my site. If these are working normally, then you'll know it's not a boydsmaps problem.
Then check NJPB maps - the 1930, 1995, 2002, 2007, 2012 and 2015 aerials also come from NJGIN. If these maps are slow at NJPB, you'll know that it's an NJGIN problem. And this was the case last night, all these maps were also very slow at NJPB.