If the file system is efficient enough (NTFS should be--or will be soon, as Microsoft focuses on SSD performance), you shouldn't need to defragment a file system on SSDs. Random seek time is the same as sequential seek time, so fragmentation in and of itself won't be a problem.
An inefficient file system, however, will have problems regardless. Some file systems may do well working with existing fragmented files but bog down when allocating new files over highly fragemented regions of free space.
