According to reports, support for the TRIM command used by modern solid-state drives (SSD) will arrive with the release of Mac OS X Lion, aka Mac OS X Version 10.7. The software improves the write performance of the flash memory and can also reduce wear on the memory cells.
The article at AppleInsider looks at the latest developer release of Mac OS X Lion. It points out that the SSDs in current MacBook models incorporate TRIM in firmware, however, the current Snow Leopard OS doesn't support the technology.
The support is a work in progress, it appears.
The TRIM command is part of the ATA interface standard. So far, it appears Apple's support in Lion is only activated for SSDs shipped by the company and not third party devices, but this is likely to be fleshed out more as Lion develops.