the reason they havn't moved to desktops yet is because its main benefits are more suited to laptops. i don't know any figures on the speed or lifetime though
Advantages * Faster start-up – as no spin-up is required. (RAM & Flash) * Typically fast random access for reading – as there is no read/write head to move. (RAM & Flash) * Extremely low read and write latency times – as SSD seek-times are orders of magnitude lower than the best current hard disk drives. (RAM) In applications where hard disk seeks are the limiting factor this results in faster boot and application launch times ( see Amdahl's law). (RAM) * No noise – a lack of moving parts makes SSDs completely silent, unless, as in the case of some high-end and high-capacity models, they have cooling fans attached. (RAM & Flash) * For low-capacity SSDs, low power consumption and heat production – although high-end SSDs and DRAM-based SSDs may have significantly higher power requirements. * High mechanical reliability – the lack of moving parts almost eliminates the risk of mechanical failure. (RAM & Flash) o Ability to endure extreme shock, high altitude, vibration and extremes of temperature – once again because there are no moving parts. This makes SSDs useful for laptops, mobile computers, and devices that operate in extreme conditions. (Flash) * Relatively deterministic performance – unlike hard disk drives, performance of SSDs is almost constant and deterministic across the entire storage. This is because the seek time is almost constant and is not dependent on the physical location of the data, and so, file fragmentation has almost no impact on performance. * For low-capacity SSDs, lower weight and size – although size and weight per unit storage are still better for traditional hard drives, and microdrives allow up to 20 GB storage in a CompactFlash 42.8Ã—36.4Ã—5 mm (1.7Ã—1.4Ã—.2 in) form-factor. Up to 256 GB, SSDs are currently lighter than hard drives of the same capacity.  Disadvantages * Price – as of mid-2008, flash memory prices are still considerably more costly per gigabyte than are comparable conventional hard drives: around USD 3.50 per GB compared to typically less than USD 0.40  for mechanical drives. * Capacity – although currently far lower than that of conventional hard drives, SSD capacity is predicted to increase rapidly, with experimental drives of up to 1 TB in test. * Higher vulnerability to certain types of effects, including abrupt power loss (especially DRAM based SSDs), magnetic fields and electric/static charges, in comparison to normal HDDs (which store the data inside a Faraday cage). * Limited write cycles – flash-memory storage will often wear out after 300,000-500,000 write cycles, while high endurance flash-memory storage may have an endurance of 1–5 million write cycles (many log files, file allocation tables, and other commonly used parts of the file system exceed this over the lifetime of a computer . Special file systems or firmware designs can mitigate this problem by spreading writes over the entire device (so-called wear levelling), rather than rewriting files in place. This problem is being improved all the time, with consequent increases in expected lifespans. Today's drives can last up to 20 years with average usage. An example for the lifetime of SSD is explained in detail here. SSDs based on DRAM, however, do not suffer from this problem. * Slower write speeds – as erase blocks on flash-based SSDs generally are quite large, they are far slower than conventional disks for random writes, and in some cases for sequential writes. SSDs based on DRAM do not suffer from this problem. * Lower storage density – hard disks can store more data per unit volume than DRAM or flash SSDs, except for very low capacity/small devices. With the introduction of smaller technology node processes, the storage density of SSDs is expected to rapidly increase in the near future.
EDIT: Yes I know that it's a combination of RAM and flash information.