I'm sure this is similar to a lot of existing bugs. I'm filing this separately to keep track of any macbook-specific tweaks which might need to be documented, if a solution is found.

This is for 11.0-CURRENT i386 -r270176 on a 13" Core 2 Duo macbook.
I'm using the nvidia binary driver, version 331.67. That's built from ports, with ACPI_PM enabled. All my testing is done at the console, without X running.

Supported states are:

    hw.acpi.supported_sleep_state: S3 S4 S5
    hw.acpi.sleep_button_state: S3
    hw.acpi.suspend_state: S3

Symptoms are as follows:

    1. acpiconf -s3; I see USB devices detach, and then the screen blanks and the fan turns off. The standby LED pulses a heartbeat. This all seems good to me.
    2. Press the standby button once
    3. The LED flashes once, brightly. Then turns off. The screen is still blank. The fan turns slowly, and gradually gets faster.

I'm using a USB wifi thing, and its LED does not come back on. Typing things appears to have no effect, but it's hard to tell. I presume the USB devices are still detached, in which case I wouldn't expect the keyboard to work anyway.

Modules loaded:

; kldstat
Id Refs Address    Size     Name
 1   39 0xc0400000 16704d0  kernel
 2    2 0xc1a71000 75144    linux.ko
 3    1 0xc1ae7000 3290     coretemp.ko
 4    1 0xc1aeb000 9ff3e8   nvidia.ko
 5    1 0xc9037000 11000    if_urtwn.ko
 6    1 0xc9051000 5000     wsp.ko
 7    1 0xc905b000 5000     ums.ko
 8    1 0xc9070000 7000     ng_ubt.ko
 9    5 0xc9079000 e000     netgraph.ko
10    1 0xc9096000 b000     ng_hci.ko
11    3 0xc90a7000 2000     ng_bluetooth.ko
12    1 0xc9238000 10000    ng_l2cap.ko
13    1 0xc924b000 23000    ng_btsocket.ko
14    1 0xc9283000 4000     ng_socket.ko
;