The Windows 7 built-in defragmenter schedule remains in effect even if the OS is installed on an SSD, however, when the event takes place, it only defrags the HDDs (if any) in the PC. For example, in the defragmenter on my Windows 7 installation, it shows that the schedule takes place every Wednesday, but with a status of "Never run" for the OS (SSD) drive and "29/12/2010" for both hard disks.
A file defragmentmentation only process will not have a significant wear on an SSD unless the drive is pretty full. The performance improvement in reading and writing will be negligible.
A file & free-space defragmentation process has a much more significant wear on an SSD, as files are moved and rearranged towards the start of the drive to leave a large solid block of free space. The improvement on read performance will be negligible. On older non-TRIM SSD models (e.g. G1 drives), you'll probably get a gain in write performance as new data will be sequentially written instead of as individual fragments to fit inside in the free spaces.
A file optimised based defrag (e.g. sorted by frequently accessed/modified) has the most severe wear on an SSD, as nearly every file on the drive is moved about such as that frequently accessed files are towards the start and large less frequently accessed files are moved to the end. Again, you may get a small gain in write performance for early non-TRIM SSD models, but you'll gain no improvement in read performance and cause a rather significant amount of wear on the SSD NAND moving a huge amount of data around.
As far as I'm aware of, PerfectDisk and most other commercial defragmentation tools use a file optimised defragmentation method by default!
On a modern SSD, defragmentation will potentially degrade the performance, as the large number of files being moved around will leave the SSD with plenty of background garbage collection to carry out from all the random write operations, resulting in lower write performance until this process is complete while the SSD is left running idle.
If you need to reduce the size of a partition on an SSD, this is probably the only time that you will need to carry out a free-space defragmentation on an SSD. In order to reduce the size of the partition, there must be no files or file fragments located between the end of the partition and where the new end boundary will be, otherwise you will not be able to shrink the partition beyond where the last file ends.