It's worth noting that those speeds are exclusive to the largest drive. The 128GB and 64GB versions run at 420MBs/210MBs and 370MBs/110MBs. The M2S series carries Marvell's 88SS9174 which Plextor hails as the world's most advanced controller. It's the same chip seen in Crucial's RealSSD C300 and it features 128MB of cache, which boosts small write performance and reduce stuttering.
The M2S series also supports Windows 7's TRIM command as well as dynamic wear leveling to help prevent the inevitable performance decrease after heavy use. Plextor will begin shipping units sometime next month, though an exact release date hasn't been announced -- nor has pricing. Drives will come with a three-year warranty and Acronis True Image for migration and backups.