It looks like you're new here. If you want to get involved, click one of these buttons!
My view for a while now has been that SSD performance is good enough. We have good controllers from Marvell, SandForce, Samsung, and now LAMD. Indilinx's upcoming Barefoot 3 controller will probably join them, and there's also the possibility that more will come out of nowhere like the LAMD controller recently did. There are still some bad controllers on the market, but there are enough good ones and enough competition at all stages that no one can gouge you with monopolistic prices.
Sure, you can run benchmarks and find that this SSD is 20% faster than that one in such and such particular scenario. But that doesn't matter anymore, at least for consumer use, as the good ones are all so fast. Debating whether you need this SSD or that one for performance reasons is like asking whether a GeForce GTX 680 or a Radeon HD 7970 GHz Edition is better for watching videos on YouTube.
Reliability still matters, but there are plenty of options that are both reliable and fast. That leaves the price tag as the only good reason to get a hard drive anymore. If you need a terabyte or more of capacity, hard drives are cheaper by more than an order of magnitude.
Initially, there was SLC NAND flash. This is NAND flash in which each cell can have two different levels of charges stored, so that the cell can hold one bit of information. NAND flash moved to MLC a long time ago, and SSDs quickly adopted it. This means cells have possible levels of charge, so that each cell can hold two bits of information. Today, there are only a handful of SLC SSDs.
TLC means that a cell can have eight possible levels of charge, which allows a single cell to hold 3 bits of information. Having 3 bits in the same space that used to have 2 bits means you an give 50% more capacity for a given cost of production. That's not going to close the price gap with hard drives all by itself, but it's movement in the right direction.
While TLC NAND flash has been available for quite a while, there are problems with reliability. Eight possible levels of charge means narrower gaps between each possible amount of charge. The actual charge on a cell is some integer multiple of the charge of an electron, of course, but the way NAND flash works is to measure the charge and then round it to a charge level that corresponds to a particular combination of bits.
The problem is that you can't have an exact charge level stay that way forever. For reasons of quantum mechanics, electrons leak out (or in) and change the charge level of a cell. If this happens to too many electrons in the same cell, reading the data later will give the wrong value. The closer the meaningful levels of charge are to each other, the fewer electrons have to leak out to give wrong data.
There are a variety of ways to combat this to some degree. There is a lot of redundancy built into NAND flash, just like hard drives, so even if one bit does get flipped, it will be detected and corrected. The state of various cells is periodically refreshed, so that even if the charge has drifted slightly from the intended value, it will be erased and rewritten with the proper charge, and usually before it can cause the wrong data to be read. That's not new to TLC NAND flash, as SLC and MLC had to do so as well.
But TLC requires more of it to maintain reliability. And SSDs are generally believed to require much greater reliability than a simple USB flash drive that you buy for $10. Losing your OS, programs, and primary copy of your data is a much bigger problem than having a USB flash drive die, since you probably weren't relying on the latter for anything critically important.
Samsung isn't the only SSD vendor that will use TLC NAND flash, of course. The cost advantage is large enough that they'll probably all jump on board soon. OCZ has been talking about it for a while already, though they commonly talk about upcoming products months before they launch. But today's public launch of the first TLC SSDs, and from a reputable vendor at that, is a major sign of progress.
As with die shrinks, Samsung says not to expect prices to crater instantly. It takes a while to ramp up production of new products. But this should eventually mean that you get 50% more SSD capacity for a given price tag than you would have with MLC flash. And that's a big deal.