Ramdisk on 3.x firmware (currently beta release) is a simple img3 file, that you can decryp using vfdecrypt keys. But vfdecryp can't decryp img3 files, so you must download command line utility called img3decrypt. For easier access, put them in /usr/local/bin
In Terminal.app enter: img3decrypt e rrestore_ramdisk.dmg restore_ramdisk_decrypted.dmg Ramdisk_IV Ramdisk_Key
Where restore_ramdisk.dmg is image of restore ramdisk (for example 3.0 beta 1 iPhone GSM firmware restore ramdisk is 018-4793-1.dmg), and restore_ramdisk_decrypted.dmg is decrypted image, that you can mount and explore from Finder. Ramdisk_IV and Ramdisk_Key is a decrypted keys that you can find in vfdecrypt page or in Info.plist from PwnageTool FirmwareBundles folder.