DDR4 is also extremely new. Expect it to get faster/better timing specs as time progresses.
DDR4 is like $350 for 4x4GB. Too expensive still. This time next year we should see prices closer to what we are paying for DDR3 today.
DDR4 is "extremely new" as in 2011. For me, the only real improvement seems to be in power consumption.
Since regular SDRAM, each DDR generation has doubled throughput, but latencies have only improved very slowly. So in many cases the doubled data rate is just a marketing gimmick. This might explain why each DDR generation has been relatively slow to enter mass market. For example, in late 2008 I was speccing a work laptop, and it had this new and shiny DDR3 memory, with all the issues such as price and availability of big-ass 4 GB SODIMMs. Later in 2010 I bought a new motherboard for home, with DDR2, so apparently DDR3 was still not for everyone.
Of course, increased throughput does help in many cases, but I especially like the reduced power consumption. So I for one welcome our new DDR4 overlords -- once they are widely available and affordable. Even DDR3 seems hideously expensive compared to other hardware -- I can get a new motherboard for less than the price of an 8 GB DIMM.