Powertop is definitely having a positive effect. Since the initial post on the Rhythmbox mailing list idle wakeups have decreased dramatically.

Rhythmbox 0.10.2

PowerTOP 1.9    (C) 2007 Intel Corporation
Collecting data for 30 seconds
Cn	          Avg residency
C0 (cpu running)        ( 0.7%)
C1		  0.0ms ( 0.0%)
C2		 39.1ms (50.1%)
C3		  0.6ms ( 0.0%)
C4		 25.3ms (49.2%)
P-states (frequencies)
1.87 Ghz     0.5%
1.60 Ghz     0.0%
1333 Mhz     0.0%
800 Mhz    99.5%
 Wakeups-from-idle per second : 32.7	interval: 30.0s
no ACPI power usage estimate available
Top causes for wakeups:
 32.3% ( 10.1)         rhythmbox : schedule_timeout (process_timeout)
32.0% ( 10.0)       <interrupt> : ipw2200, lan0
8.9% (  2.8)       <interrupt> : acpi
4.6% (  1.4)    wpa_supplicant : schedule_timeout (process_timeout)
3.4% (  1.1)           gkrellm : schedule_timeout (process_timeout)
3.4% (  1.1)                 X : do_setitimer (it_real_fn)
 3.3% (  1.0)         rhythmbox : futex_wait (hrtimer_wakeup)

Rhythmbox 0.11.2

PowerTOP 1.9    (C) 2007 Intel Corporation
Collecting data for 30 seconds
Cn	          Avg residency
C0 (cpu running)        ( 0.5%)
C1		  0.0ms ( 0.0%)
C2		 66.8ms (75.3%)
C3		  0.4ms ( 0.0%)
C4		 22.2ms (24.2%)
P-states (frequencies)
1.87 Ghz     0.0%
1.60 Ghz     0.0%
1333 Mhz     0.0%
800 Mhz   100.0%
 Wakeups-from-idle per second : 22.6	interval: 30.0s
no ACPI power usage estimate available
Top causes for wakeups:
51.0% (  9.9)       <interrupt> : ipw2200, lan0
11.6% (  2.3)       <interrupt> : acpi
7.0% (  1.4)    wpa_supplicant : schedule_timeout (process_timeout)
5.5% (  1.1)                 X : do_setitimer (it_real_fn)
5.3% (  1.0)           gkrellm : schedule_timeout (process_timeout)
2.6% (  0.5)           wpa_cli : schedule_timeout (process_timeout)
2.6% (  0.5)          events/0 : ipw_gather_stats (delayed_work_timer_fn)
2.4% (  0.5)       <interrupt> : ide0
1.5% (  0.3)          nautilus : schedule_timeout (process_timeout)
1.2% (  0.2)   gnome-settings- : schedule_timeout (process_timeout)
1.0% (  0.2)              init : schedule_timeout (process_timeout)
1.0% (  0.2)    mapping-daemon : schedule_timeout (process_timeout)
1.0% (  0.2)     <kernel> : page_writeback_init (wb_timer_fn)
1.0% (  0.2)           ifplugd : schedule_timeout (process_timeout)
    1.0% (  0.2)         rhythmbox : schedule_timeout (process_timeout)