I just did this (replace an Apple SSD with a third-party SSD). I'm not at all familiar/good with hardware of any kind, and I found it to be not that bad. The Apple 120G SSD drive I took out I believe was a Sony. I replaced it with an OWC 240G, which supposedly "wears" better over the long run and the model I picked has a 5-year warranty. By the way, I'm not connected with OWC in any way, but they seem to have similar goals as this site does, just coming from the "for profit" point of view.
The new disk does connect at the laptop's full SATA III speed (6G bits/sec), which is better than the Apple SSD, which always connected at the lower SATA II speed (3G bits/sec). I verified the connection speeds with the System Profiler utility, running it both before and after the change.
Watching their installation video convinced me that I could do it, which is saying at lot. The URL is:
Also, I believe the Apple warranty states that you can change the memory and the disk and still be OK. The booklet that comes with the laptop even has a section on upgrading the machine by changing the memory and/or the disk.