MacRumors reports Apple has quietly downgraded the SATA interface of its MacBook Pro notebooks, old models had SATA 3Gbps support while new models use the old SATA 1.5Gbps interface. Users of hard disk drives may not notice the difference, but it will affect the performance of fast solid state disks.
The slower SATA interface is unlikely to affect the bulk of users as even the fastest traditional hard drives are unable to saturate even the 1.5 Gbit interfaces. However, if you are planning on buying a fast Solid State Drive (SSD), it could affect the drive's performance. The downgrade of the interface in the new MacBook Pro has also been confirmed in early benchmarks using a fast enough SSD.