The Mac maker's most recent 13-inch MacBook Pros display an option for TRIM support in their system profilers on SSD-equipped models, one which isn't present in either the second-generation unibody 15-inch MacBook Pros or the latest refresh sporting Intel's Core i5 and Core i7 processors.
TRIM is essentially a command that lets operating systems like Mac OS X inform SSDs of which blocks of pre-written data are no longer in use, allowing them to be wiped clean internally.
This form of garbage collection overhead prevents the slowdown in future write operations on those data blocks that would otherwise result in unanticipated progressive performance degradation of write operations on the SSD over time.
It's believed that the new Nvidia GeForce 320M chipset inside the 13-inch MacBook Pros is responsible for supporting TRIM at some level. Earlier MacBook Pros employ a previous generation Nvidia chipset that lacks the same support, as does the Intel-based chipset in the most recently released Core i5 and Core i7 models.
That said, the current Core 2 Duo-based 13-inch MacBook Pros are likely among the last Macs to adopt a Nvidia chipset given that future models will employ Intel's latest chip offerings, for which the chipmaker has forbid Nvidia from supporting through its own hardware.
Update: One AppleInsider forum member notes that the same "TRIM Support: No" showed up on his Core 2, 17-Inch MacBook Pro after he updated the firmware on his SSD to version 2CV102HD.