I have an OCZ Vertex 2 for 3 or 4 years now (don't really know) and it still works (60gb)
On topic: Sleep mode could cause excessive disk writes if you have a lot of RAM and a small SSD, (for example you have 16GB of RAM and a 60GB SSD, each time it would go to sleep and save the RAM on disk, there'd be write access for whatever much memory used at the moment which can accumulate.) iirc. SSDs can only take up to 10,000 write cycles per cell.