The DS209+ has an 800 MHz CPU and 512 MB of RAM vs. a 500 MHz processor and 128 MB of RAM in its DS207+.
Both products also have 3 USB 2.0 ports and 1 eSATA port. Synology specs the new NAS at 42+MB/s for read and 36+MB/s for writes for Windows file copies (XP2, RAID 1, gigabit LAN with 9K jumbo frames).
The new NAS runs Synology's Disk Station Manager 2.0 with a feature set that includes scheduled local and network backup, UPnP AV and iTunes media servers, AD/NT domain support and SMB/CIFS, NFS and AFP network filesystems.
The DS209+ will be available in December. Pricing will be announced next month.