But isn't the point that SSD's are just memory aren't they? And with no moving parts to spin up/down and start/stop etc what would it matter how much they got used? Sorry I'm not up on stuff inside the boxes, I just look at them from outside the casing!!!
Memory - yes. Just memory - no.
Normal volatile Static RAM (the sort that forgets if you turn the power off) is just a logic circuit that can be a 0 or a 1 (what we call a bistable) - but lots of them of course. Very fast, but need juice. Dynamic RAM is a variation where the 0s and 1s are levels of charge stored on a minute capacitor. The storage element is much smaller than for static RAM so huge memory capacities are possible (these are used for the gigabytes of memory in a PC), but the charge leaks away from the capacitor over a short period of time so there has to be a frequent refresh cycle to keep restoring it.
SSDs and USB sticks use non-volatile technology. They work a bit like dynamic RAM in that the data is stored as charges, but the charge does not leak away because it is injected into a highly insulating material and then read by sensing the electric field it creates. The problem is, how do you inject charge into an insulating material (and clear it out again to erase it)? The write mechanism is a bit like an electron gun in a CRT, except in the CRT the electrons only have to cross a vacuum.
The electric fields required, and the ablating effect of the passage of high-energy electrons, are a wear mechanism and the material can only put up with so much of it before it loses its properties and goes leaky. Hence there is a limit on the write cycles, typically 100,000. SSDs have built-in mechanisms to redirect writes to different sections each time, so that the wear is shared out ("wear levelling"), and this can help a lot, but they also impose a performance hit as the SSD fills up.
In summary then: blisteringly fast for reads, relatively slow for sustained writes (OK in bursts because of caching), and dubious lifetime in continuous write situations (like a PVR).