The new Synology DSM 2.2 firmware permits (among many other new features) to use your NAS as a Time Machine destination to store Mac OS X backups. Here's how to configure it:

• Connect to your Synology Disk Station Manager
• First create a shared folder, name it whatever you want (TimeMachine in my case)
• Then enable the AppleTalk protocol and choose your previously created shared folder as Time Machine destination
• Open Time Machine preferences on your Mac and choose your NAS disk
• That's it, you're done!

As with any Time Capsule appliance, perform your first full backup over a wired link. It will take some time. Afterward, incremental backups are no problem over WiFi.