gistfile1.lua

function client_opacity_set(c, default, max, step)
        if c.opacity < 0 or c.opacity > 1 then
                c.opacity = default
        end

        if c.opacity * step < (max-step) * step then
                c.opacity = c.opacity + step
        else
                c.opacity = max
        end
end

clientkeys = awful.util.table.join(
    -- insert other clientkeys here ...
    awful.key({ modkey,           }, "Up",     function(c) client_opacity_set(c, 1, 1, 0.1) end),
    awful.key({ modkey,           }, "Down",   function(c) client_opacity_set(c, 1, 0, -0.1) end),
)

awful.rules.rules = {
    -- ...
    { rule = { class = "Pidgin" },                                               
        properties = { tag = tags[rule_screen][3], opacity = 0.9 } },
}