Bukkit

The config got a bit complicated because of some recent additions so i´ll also explain how the final speed multiplier is calculated below.
Please do not copy these examples to your config, they have not the right structure.

config.yml

hooks:
    permissions: Permissions
    # which permission system to use
    # possible values: permissions, bukkit, op, default (= op || bukkit)

worlds/your_world_name.yml

The world configs now contain sections for each event that can be used. For this example i will only show the settings of one event. Event specific config part:

items:
    enabled: true
    # if items should be needed for speedwalk

    data: 288|1|1|1, 2256|2|1.7|1.3
    # which items can be used to use speedwalk? format:
    # itemID|DecreaseBy|multiXZ|multiY, [...]

blocks:
    enabled: true
    # if blocks should be checked for a speedup

    data: 43|4.0|0.5, 44|4.0|0.5
    # which blocks allow speedwalk and what multi do they have? format:
    # blockID|multiXZ|multiY, [...]

And these settings are not event (but world) specific:

multiplier:
    enabled: false
    # if permission based multipliers should be enabled
    # BE CAREFUL: when you enable these and have a "*" permission because
    #             you are an admin you get all of the default permission
    #             multipliers at once which will launch you into the sky
    #             to die a shameful death.
    permission1:
    # one of three permissions you can set. you can define the permission
    # node names yourself. values are multipliers. 
        node: speedwalk.doubleboth
        multiY: 2.0
        multiXZ: 2.0
misc:
    multiXZ: 3.5
    multiY: 0.5
    # if you disable both items and blocks these multis are taken

Final speed calculation

In all cases the resulting speed for x and z axis gets multiplied with the player velocity. This means you get more speed when you are already walking on use.

"itemMulti" is the multiplier set for the corresponding item if matched. "blockMulti" is the multiplier set for the corresponding block(under player) if matched. "permissionMulti" is the multiplier set in the config when multipliers are enabled and the player has the according permission.

Items are enabled, blocks are enabled

finalSpeed = itemMulti * blockMulti [ * permissionMulti ]

Items are enabled, blocks are disabled

finalSpeed = itemMulti [ * permissionMulti ]

Items are disabled, blocks are enabled

finalSpeed = blockMulti [ * permissionMulti ]

Items are disabled, blocks are disabled

This is the last example and a little special case. The speed value is not taken from items or roads here as they are disabled. Set the speed values in config under misc -> multiXZ and Y.

finalSpeed = configMulti [ * permissionMulti ]