The lines in the VMX file relating to USB are as follows:

usb.present = "TRUE"
ehci.present = "TRUE"
usb.vbluetooth.startConnected = "TRUE"
usb:1.present = "TRUE"
usb:1.speed = "2"
usb:1.deviceType = "hub"
usb:1.port = "1"
usb:1.parent = "-1"
floppy0.present = "FALSE"
usb.generic.allowHID = "TRUE"
usb.autoConnect.device0 = ""
usb:0.present = "TRUE"
usb:0.deviceType = "hid"
usb:0.port = "0"
usb:0.parent = "-1"


Log file when I manually connect the keyboard:

2012-07-05T13:12:38.589+10:00| vmx| I120: USB: Connecting pattern [path:10/15/4/2 version:2] controller []
2012-07-05T13:12:38.589+10:00| vmx| I120: USB: Connecting device 0x2fa4200005ac0220
2012-07-05T13:12:38.589+10:00| vmx| I120: MsgHint: msg.msg.usb.generic.allowHID
2012-07-05T13:12:38.589+10:00| vmx| I120+ This VM is trying to claim 'Apple Keyboard'. If you continue, the device will no longer be usable in the host.---------------------------------------
2012-07-05T13:12:38.602+10:00| mouse| I120: VTHREAD start thread 10 "mouse" pid 3511
2012-07-05T13:12:38.605+10:00| keyboard| I120: VTHREAD start thread 11 "keyboard" pid 3511
2012-07-05T13:12:38.957+10:00| vmx| I120: USB: Adding autoconnect pattern [path:10/15/4/2 autoclean:1] in slot 0
2012-07-05T13:12:38.996+10:00| vmx| I120: USB: Device [name:Apple\ Keyboard vid:05ac pid:0220 path:10/15/4/2 speed:low family:hid,hid-bootable virtPath:usb:3 version:2] should already be connected
2012-07-05T13:12:38.996+10:00| vmx| I120: VMXVmdbLoadUsbDevices: New set of 7 USB devices
2012-07-05T13:12:38.996+10:00| vmx| I120: USB: Found device [name:Apple\ Bluetooth\ USB\ Host\ Controller vid:05ac pid:8206 path:10/1/1 speed:full family:wireless,bluetooth version:2]
2012-07-05T13:12:38.996+10:00| vmx| I120: USB: Found device [name:Apple\ Optical\ USB\ Mouse vid:05ac pid:0304 path:13/1/1 speed:low family:hid,hid-bootable version:2]
2012-07-05T13:12:38.996+10:00| vmx| I120: USB: Found device [name:Apple\ IR\ Receiver vid:05ac pid:8242 path:13/5/1 speed:low family:hid version:2]
2012-07-05T13:12:38.996+10:00| vmx| I120: USB: Found device [name:Seagate\ RSS\ FreeAgent\ GoFlex vid:0bc2 pid:5021 path:10/15/2 speed:high family:storage version:2 serialnum:NA0B5405]
2012-07-05T13:12:38.996+10:00| vmx| I120: USB: Found device [name:Apple\ Built-in\ iSight vid:05ac pid:8502 path:13/15/4 speed:high family:vendor,other,video version:2 serialnum:D0671E920E870A49\ (03.01)]
2012-07-05T13:12:38.996+10:00| vmx| I120: USB: Found device [name:Apple\ Keyboard vid:05ac pid:0220 path:10/15/4/2 speed:low family:hid,hid-bootable virtPath:usb:3 version:2], connected to [Virtual Hub 1, Port 2]
2012-07-05T13:12:38.996+10:00| vmx| I120: USB: Found device [name:Virtual\ Bluetooth\ Adapter vid:0a12 pid:0001 speed:full family:wireless,bluetooth virtPath:usb:2 deviceType:virtual-bluetooth version:2 info:0000000], connected to [Virtual Hub 1, Port 1]
2012-07-05T13:12:39.875+10:00| mouse| I120: Forgetting VThreadID 10 ("mouse").
2012-07-05T13:12:39.877+10:00| keyboard| I120: Forgetting VThreadID 11 ("keyboard").