Thanks to sound advice on these forums, I am a happy owner of a new system with a Crucial M4 128 GB SSD. I am thrilled with the performance so far.
This is a home pc (A non-gamer "office pc") that I use for playing with software and web browsing.
I have installed windows 7 as the primary OS on the PC. The OS and some software (Office, visual studio, eclipse, etc) on the SSD.
In addition, I have also installed windows server 2008 in a 40GB virtual disk on the SSD.
So far I have used up about 72 GB of the SSD. Approximately 32 GB for the windows 7 and software and a large 40GB file for the virtualbox disk. I have been careful to save photos and videos to a data disk (seagate 7200 rpm HDD).
How much of a free space should I leave on this SSD to ensure proper level wearing?
There's no one number. The drive will work if it's 100% full because there is some "hidden" space kept aside for wear levelling. But the more free space you leave, the longer your drive will ultimately last. The more writing you do to the drive, the better it would be to leave more space free.
For normal desktop usage, your SSD will be obsolete long before you run out of update capability.
The vendors reserve space for reserve anyway.
If, by any chance you run out of updates, your ssd will still be readable, allowing you to copy it over to a larger drive.
Not to worry. Enjoy.