They're great for circulating both cool and warm air, so AC and heating costs can actually be lowered quite a bit.
Make sure you flip the reversing switch during the cold months when heating is running. When it's running backwards you won't feel the air movement on your skin. The air movement on your skin is what causes the fans to have an apparent cooling effect.
Probably best to buy now if you are in the market.
As an electrical engineer I begrudgingly welcome this rule change. It's really frustrating that we need government regulations like this to push energy efficiency standards, but that's the world we live in. Businesses really don't push these limits on their own unless a product is battery powered, and that's the most frustrating aspect. We have the technology. It's cheap. But they'd rather save $5/unit :-/
Buy now if you need ceiling fans (that's worth it due to the energy savings regardless). In a few years, if you still need ceiling fans (because you moved, etc) the fans you buy will be even cheaper to operate. Just like the newer microwaves, window A/C, and mini-split systems, these new ceiling fans will most likely be "inverter" style, using a quieter high efficiency 3-phase DC motor. These aren't expensive systems; the motors were already developed many many years ago and have had steady efficiency gains driven by use in brushless power drills, eBikes, diesel freight trains, electric lawn mowers, etc. If you can find an inverter drive ceiling fan you like, buy that now; there's a few on the market, but not many.