So basically you will see DDR4 start at DDR4-1600 speeds, and increase to DDR4-3200 speeds within a year or two. As time goes on, the higher level speeds will come down more and more in cost. The first module Samsung produces runs at DDR4-2133 speeds. The new RAM will use a standard voltage of 1.2v, compared to most DDR3 RAM that uses 1.5v and 1.65v My estimate: It will probably be between Q3 of 2012 to Q1 of 2013 before DDR4 becomes the standard for all new computers. Samsung said they will release DDR4 into production in early 2012, after which Intel and AMD will introduce a new processor that features both a DDR3 and DDR4 memory controller, and you will need to buy a new motherboard with the DDR4 RAM slots to be able to use DDR4 memory. Prices will be high at first, but will probably start to slowly go down in mid 2013 once production from all major companies has been fully ramped up. Also worth noting that these new RAM sticks will not increase your speed in most cases as the timings will follow the same as it has been from the very first generation of DDR. Latency will remain the same as it has been since the late 90s, you will only increase the total bandwidth. Meaning you can push more data through per second.
IMO DDR1 was the most exciting, DDR2 was definitely second though to me. With DDR1 we got double the data rate we previously had, and overclocking was really fun back then. It is still hard to beat the speed performance of great DDR1. My best back then was DDR-523 with 1.5-2-2-4-1T timings. Scale that up to modern DDR3 speeds and it would be exactly the same latency as: DDR3-2092 with 6-8-8-16-1T timings! It will be really fun to have complete overkill DDR4-3200 in a computer someday soon. The big thing I am looking forward to with DDR4 is 8GB and 16GB sticks of RAM