RFTs have their place, but many owners are infuriated by hard ride, high replacement cost, spotty availability and, in some cases, low tread life. My personal preference is for a spare. That would be the case even my car had RFTs.
Adding a spare to the trunk is sketchy, as you'd have to tie it down somehow. Easier to deal with are the jack and tools you'd need to carry.
There are many cars on the road today with no spare and no RFTs. The new Pontiac G8 GT is a prime example. It has no spare and standard tires. Corvette, 2008 Viper, Ford GT, Lotus Elise--all of these have the same setup. There are others. What they all have instead is a what is sometimes known as a Continental Kit: a small compressor and a can of high-grade tire sealant. (Named for Continental, the tire company that supplies many automakers with these kits; not for the 50's spare-on-the-bumper trick.)
You still have to stop to use the kit, and it won't help with a sidewall gash or a large hole. But if you are a AAA member and pay regular attention to your tire pressures and react swiftly to your TPMS light, you should be covered in most situations. That said, I'd still want a spare in my trunk for long trips in rural areas.